Triumph Repair: engine / tranny match-up, Spitfire, overdrive

Question
I have an 1974 spitfire and tranny with overdrive, but no engine.

I also have a 1977 1500 and tranny, but without overdrive.  I want to drop in the 1977 1500 (minus the smog)and use the 1974 tranny because it has the overdrive feature.  Is this a good idea?.  

The bolt pattern on the bell housings match up, but the clutch plate doesn't.  The spline pattern on the 1977 clutch plate is smaller than the spline pattern on the 1974 tranny.

What do I do?  Do I just need to buy a 1974 clutch plate?  Are the throw-out bearings and pressure plates the same, or do I need these as well?
Thanks
ED

Answer
Ed,

You can use the '77 engine in the '74 chassis, as long as you fit a '73/74 US spec 1500 clutch disc.   Not a terribly bad idea to renew the pressure plate and throwout at the same time, but pulling the trans in a Spitfire isn't a really bad job if they prove bad.

Just be sure that whatever supplier you're using understands you need the large diameter 10 spline clutch disc from the 1500, not the 1300 disc.

You'll also need to juggle the wiring a bit to accomodate the distributor, if the '77 engine  still has it's Lucas electronic ignition.   Also, the '74 chassis should have a mechanical tachometer, the '77 was fitted with an electronic unit.

If you find the '74 o/d trans is defective you can at least fit the '77 single rail trans in it's place.   No need to find a new driveshaft.



Cheers,

Jim