It is possible. Level of difficulty depends on whether the Spitfire box is a three rail one (ie late 1300) or the single rail (flat-top) one from a 1500.
If it's one of the fairly rare 3 rail + J-type, it's pretty straight forward. You use the casing, mainshaft and OD from the Spitfire and the gears including layshaft and input shaft from the GT6 combining the best synchros from the two. The gearbox will end up the same length as the normal GT6 D-type OD box. (there may also be a few factory J-type equipped GT6s out there - subject of argument!)
If a single rail then it gets harder. The single rail mainshaft tip is larger than the 3 rail so your GT6 input shaft would need machining work to take the bigger spigot bearing. The alternative would be to use TR7 4 speed gears and input shaft which will work with that mainshaft. Use the TR7 clutch plate to match.
The single rail OD box is 1" longer due to longer mainshaft and adaptor housing so you hybrid gearbox will be too. Still fits, but pretty tight at the back and you'll need a shorter, non-standard propshaft. This box will be a bit stronger though.
Cheers
Nick
--Previous Message--
: I have a GT6+ engine and non-OD GT6
: tranny that I plan on putting in my
: 1979 Spitfire this winter. I also have
: a complete Tranny with J-Type OD from a
: Spitfire. I would like to add the
: J-type OD to the GT6 tranny. Anyone do
: this before? What is involved? What
: would be a good Diff ratio to work with
: this combo? I think I have a 3:89 in
: the Spitfire with OD. Thanks,
: Mike Mack
: 79 Spitfire
: 73 Stag
: 80 TR8
: 76 TR7
:
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