what is wrong with the gt 6 drive train , lets start at the front rad is too small needs to be 3 times bigger
 the engine is a good engine but for street use 200 hp is about max (our s had between 240 and 250 hp at 8600 rpm  but idled at 1000 rpm not very streetable.  the trans in racing would go through 3 out of 4 sycros in a race weekend if the gear box lasted.at all.   the drive shaft and axle ujoints are too week for a stock eng torque and the stub axeles and axles get the boobe prize for being almost as week.  If you want to see why I know this this is a picture of a triumph vitesse (gt 6 sedan)  built to compete in the under 2.5 ltr trans am racing around 250 hp with a top speed at the track of 155 aprox mph . thats what is wrong wiyh the gt 6 drive train.
mark thompson

If you ware wiling to go with a GM Ecotec motor you may get lucky and find a totaled Solstice or Sky somewhere. It is a aluminum motor and should have a smaller auto trans (not sure how small) They put out a good amount of HP and would be better for a even more light weight car.

I just picked up a Rover 4.0 with an automatic transmission and transfer case. The auto transmission is rather skinny. Wouldn't that fit between the rails of a Triumph?

I don't know if there is a proper tailshaft for that version of transmission, one that will take a slip-yolk of a driveshaft.

So, a v8 WOULD upset the "factory balance"; it's too damn light!

I just found this thread, so sorry for coming into it late.
Another option for an automatic is a GM 4l30E. Overdrive in 4th. This tranny came on Cadillacs, Isuzu's, and BMW's. Fabled German engineering, designed in Detroit, and built in France. :0)
You can find it with a GM V6 bolt pattern on the bell housing.
It got a reputation as being weak in the Isuzu Troopers. That car should have had the 4L40E I think.
The pans are still wide for a Spit frame rail and mods will be needed. It isn't as wide as the others though.
Here is a PDF spec sheet:
http://www.unofficialbmw.com/images/BMW_Automatic_4L30E.pdf

I'd suggest forgetting a V6 or V8 conversion (V6s are nasty, heavy, complex and don't have the vibration-free balanced nature of a straight-six, and a TR6 just isn't a TR6 with a V8) and do one of the following:

 - Rework the existing straight-six engine
 - Drop in a BMW straight-six (it's been done, there's a TR6 somewhere with a BMW S54 3.2L straight-six from an E46 M3)
 - Drop in a Toyota/Lexus 2JZ straight-six
 - Drop in a Nissan RB-series straight-six

Four-cylinder engines tend to sound dull - the Honda S2000 motor is one exception, mind. Just as long as it revs freely, growls as it does so, and (ideally) pops and bangs on the overrun... Alfa Romeo engine, anyone? There's a 156 in every scrapyard round my part of the world... mind you, I'm on the far side of the Atlantic from most of you, it'll be much harder to get an Alfa motor over in the US!

I believe the honda engine requires you to use the honda factory dash. Google Minx with s2000 motor and you will find a guy putting one in a hillman minx. Awesome build. An RB motor is an engineering work of art, you can get massive power from those, as well as supra engines. The RBs get gobbled up pretty quickly here by people putting them in old Zs. That makes for a beast of a car, a few bolt ons and you have 450 hp. Theres one on youtube that will walk away from a hennessey viper like it has my grandpa driving it. Theres an MGB on youtube with a supra engine on it, maybe you can get in touch with the guy for help, i think hes in Arizona? But a straight 6 would look perfect in there.

Whatever engine and trans you select, consider most automatics will have too wide a lower pan to clear the frame rails without some modification and reinforcement. That Spitfire/GT6 frame is pretty narrow in the transmission area. The original 4 speed is pretty small and couldn't drop out from the bottom, has to come out from the interior side.

placing a 1993 chevy S10 V6 2.8 in a 80 spitfire, after ive converted it to a carb setup, (old school) from the trottle setup,  with a T5, hoping not to make any mods to the firewall,  ive read that the oil pan has to be modified?  in what way?

Are you still there ? I'm not on a rant, so maybe I can address your original question ? How about an automatic transaxle ? Lot's of them out there. You might want to look at those with a rigid mounted torque tube, between the engine and t-axle. Porsche 924/944 ? 928= too large, for your app. I suspect Jim Nichols(this site), knows of many more potentials.  Come on clan, let's focus here. Good Luck David, roverman.

There is an Australian lockout (for RWD)and cover for the Subaru Impezza/Outback AWD transaxle. Used in Beck Porsche Spyder mid-engine. It could be used in rear drive with Torque tube like 61-63 Pontiac Tempest, but seriously I would widen the mid section of the frame and use a 200R4 with Speedway Motors adapter to 60 degree V6. I would then use the Toyota IFS diff in the rear. I have done a article on this site.     http://forum.britishv8.org/read.php?3,22861