I decided to treat myself to the Aston filler cap from Chris at Brasscraft along with the filler hose and clips etc from CBS. The filler flange that the Aston cap attaches to i had already got from Brasscraft last year. Allot of people do say that Chris's products are expensive (and i agree they are) but they certainly have a top class quality to them, and you would be hard pushed to find a better quality item, so worth the money in my opinion.
I intended to initially bond the filler flange to the body as so that no fixings were visible and kept with my "clean lines" theory that i was wanting to achieve. This plan sharp went out the window when the filler hose arrived. I ordered the heavy duty filler hose rather than the super flex stuff as i was trying to avoid fuel vapour smell in the boot once completed. However the heavy duty hose is so rigid that the amount of pressure it would put on the filler flange meant that it would never have bonded in a million years, so drill the flange and countersink the heads.
First job was to cut the access hole in the inner wing so the hose can pass from the cap to the tank. Not an enjoyable task to be honest, as the hose is very rigid so not easy to flex through the gap, and when cutting the hole i wanted it to fit nicely, rather than to big. Once the hole was cut it needs to be edged with some off cut of rubber bonnet seal. After paint and IVA i will seal round the gap with some silicon to stop the weather invading the boot area. I have also cut the hole big enough for the filler breather pipe which is just a length of 10mm fuel hose.
With the hose roughly cut to length its just a case of trial and error, until the correct length is achieved. You need to take care that you cover the filler of the tank as so to stop any crap or crud falling in as your working. I found it best to secure the top flange with the locking insert as so that end was sealed and then offer it down through the wing onto the tank. 
With the length pretty much done, now was time to drill and fit the top flange. Chris machines in the fixing positions equally around edge so its just a simple case of drilling through and then counter sinking the heads of the screws. When you get the filler cap you will also get some paper washer/gaskets that fit into the cap and will adjust the lock down position. So if you need to rotate the cap a bit you can just insert x amount of washers and it will reduce the amount of rotation before locking out. After checking with AK regarding this i was advised not to use any of the washers/gaskets so that the cap screws all the way down onto the flange. This is to do with the final height and orientation of the filler for IVA requirements.
When it comes to the screw/bolt heads i ordered stainless steel socket heads so that they fit the recess nicely and fixing using an allen key. The only way i was able to cut the countersunk recess was with a larger drill bit then to slowly open up with the dremmel. I do have a bit to do it but with the threads for the filler cap it would have made a terrible mess of the polished finish. Overall it looks ok, not perfect, but not noticeable unless you really look, and half the heads are covered when the cap is screwed down. So move on to fitting the flange to the body.
Before any cutting and drilling the cap needs to be screwed down and roughly put into position. You need to make sure that when the cap is open that it doesn't flip back and touch the bodywork, same with the release clip. This is something i hadn't even considered until i checked with Wendi at AK. Imagine getting the car all painted and then when you open the cap you chip the paint i would have been gutted!!
The cap needs to be rotated clockwise as much as possible before it touches the body on the hinge and release clip. Again this is to comply with the IVA regulations on radius i believe. I was speaking to a mate Paul the other day regarding this and i fear i will have to rotate mine more (i had already drilled and fixed) as he was saying that the cap hinge needs to be pointing towards the passenger side windscreen post in order to achieve the required angle for IVA compliance. Mine is more towards where the passenger side roll bar leg would be (if i had one) So something i will have to possible adjust prior to IVA. I'll keep you posted.
Fitting the flange is just a simple task of drilling through the body to fit. This is why it is important to finalise the position of the filler cap first with regards to it touching the body, as the fixing holes will obviously be in a required position. Also i was sure to cover the filler hose prior to drilling through the body as you don't want fibreglass dust down in the tank!! Also another tip i thought of when fitting, don't let your neighbour stand watching you next to an open fuel tank with his lit cigarette in hand!!! haha fuel vapour is allot more volatile than the liquid itself!! Just ask "Tony M" of the Cobraclub forum.... he has a great knowledge of fuel tank vapour and explosions!!!
So all fitted and complete you will see that the cap also has a locking insert which i have been told is not actually required for IVA as the Aston cap itself has a seal. I personal will just leave it in i think, its no hardship to undo when filling up, and will mean i have to remove the key from the ignition in order to fill up. I have also got a unleaded fuel restrictor in the cap, as so that if the diesel pump is picked up by mistake it will not fit the filler. I have never in my life miss fuel but i sure as hell don't want my Cobra to be the first time and my daily drive is diesel so "belts and braces" technique again. 
I'm happy with this overall and all that is left to do is to fit a one way valve to the breather hose to allow the tank to breath in the hot summer. This will just be running up the filler hose and secured above the fill level under the flange. I will also be running an earth cable from the filler cap down to the chassis, as so to reduce the risk of static spark when filling up, this will simply be a ring terminal off one of the fixing bolts down to chassis... job done!!! Next on the list.... save shed loads of money for wheels and tyres!!!! so expect an update in 2015!!
