The FIA has a slightly larger tank than the standard car but also its filling point is not n the centre of the car but off to the drivers side. Gerry supplied the SS tank to me, it was also collected n the round trip to Cornwall.
The process to find the correct location is clearly written out in the manual. It is a combination of ensuring alignment with the filler cap and securing to the bulkhead. I discovered that the bracket positions can effect the ability to align to the filler cap. In the manual it explains that you should not use nylon nuts during this process as you will remove them multiple times.
During this process you drill a small pilot hole in the position marked on the body for the fuel filler cap. The pilot hole should be large enough to place a knitting needle through. Placing tape to cover the fuel filler in the tank you can then place the tank in the car fully fitted and use the needle to mark the relative position of the hole to the centre of the filler on the tank.
In my case the location was pretty much spot on! I took that as a good sign. Now that I was comfortable I had the tank in the correct place I could drill out the filler cap and fixings holes.
In the manual Hawk recommend taping these holes which is just as well because the bolts supplied only just make it through to the other side so fitting the nuts would not be easy! I may still do some of them in the end once the car is painted.