After checking the Ford parts catalogue and asking a friend of mine who has owned a lot of MK4 and has an EFI one right now I know a little more.
The inner wings and therefore the header tanks were modified 1989 when the EFI CVH was introduced. The non-EFI header tanks (sitting on the drivers side) won't fit the pre-89 cars/shells as these tanks are higher. Funny thing is the EFI header tanks had the same shape as the pre-89 tanks (the ones mounted to the right / UK drivers side). Only difference is the position of the hose connectors. These sit slightly to the left or the right side but the hoses should be long enough.
Cheers some good info there,Im thinking one of these would fit, maybe have to drill some holes to mount.
https://www.autospecialists.co.uk/pr...s-turbo-s1-s2/