changing spitfire gear sets

["Tom Britt" <zhbmacaw@worldnet.att.net>]

Friends:

    I am attempting to change my 73 spitfire, rear end gear ratio from the
stock 3:89 to a 4:11. I have a 4:11 ring and pinion from a 63 mark III, was
told it would match up, but it doesn't. I am a low budget vintage racer and
looking for advice to solve this problem.
    Any help would be greatly appreciated.
I also have a 4:55 ring and pinion, to low a gear for our track, probably good
for autocrossers, if anyone interested.

            Tom Britt
            Spitfire racer