Option A: :idea:
The best option is to use an easily reversable transmission unit like a PowerGlide 2-stage from a Ch**y Corvair! I think Corvairs used them. Remember the Corvair engine ran anti-clockwise, so:-
1. use the Corvair auto case set up for the standard 250 I6, using an adaptor plate.
2.Then you have to use a reverse of the stock engine details so it will work
backwards. The pistons need to be reversed, the bearings, and the stock ignition needs to be ditched for a GM 3800 trigger system.
3.The oil pump drive has to be reversed and checked for operation in a reverse state. The spaggheti drive from the dissy needs to be replaced or used as a hall-effect trigger or cut-out wheel for the GM 3800 ignition. Its got to behave the same way as the distributor shaft did.
4. The cam drive has to be changed to ensure it doesn't run out of oil. Then the cam itself needs to be re-timed and you just got to hope the reverse rotation doesn't upset the lifters...shouldn't be a problem!
5. The differential carrier in the Corvair was driven by a layshaft, I think, from the back of the Covair tranny, but I'm not certain. This offers the possibility of a) second hypoid bevel gear back to the front transmission, just by having a SG iron casting made with a stock bevel gear or b) a continuation of the stock RWD/4WD Turbo~Hydramatic transmission extension housing forwards to a front PowerGlide tranny.
6. At the front, just use the stock RWD PowerGlide with an adaptor to suit the front 250 engine.
7. A centre CV joint or centre diff lock could be used to minimise the prospect of drive shaft wind-up.
8. For the rear axle, use a Alfa Romeo or Volvo 344GLT deDion axle or a transverse leaf off a Corvette. A similar chassis rail set up to the Corvair should be used.
9. Radiator can be just a couple of serial ricer number from a 2 liter front drive car mounted in the back seat like some 32 Ford drag cars use.
This allows you to run one diff, the same ratios front and back and synchronise the engines mechanically. Its still rear wheel drive!
Problem is the extra 700-850 lb of weight would kill the extra performance! And although its nothing to get 200 hp out of a 250, 400 hp in a car weighing 3700 hp may tax the diff a little more than you'd like!
Alec Issigonis, the Cypriot Greek/Turk who designed the Austin Mini, did a couple of twin four 78 cube 4WD Mini Mokes for the Ministry of Defence. They killed one driver, and were never seen again . There were two transverse engines in it, with no link between them asside from the throttle.Just plain scary!
Option Two: :idea:
Get two Ford Explorer 4 liter engines and 5-spped auto trannys. Mount one standard, the other reversed in the back. Drive both sets of wheels via the IFS diff centres from a SUV and halfshafts AMC's 1980 four wheel drives. Convert the front end to the 1980 AMC Concorde front uprights, and at the back use a stamped deDion beam such as post 1975 Alfa Romeo GTV 2000 or front beam axle like a flattie Ford with proper semi-ellictics, but with special uprights from the Alfa. The real clincher is that the 4WD would be on all the time via a drive shaft from the back of each transmission to a centre diff. This diff would have to have an idler gearset or a heavy duty plantary drum clutch to reverse the drive from clockwise to anti-clockwise. An Art Carr Powerglide or C6 hub should do the trick, but it has to be the top gear drum.
I'm not certain how the above would exactly, but I think a mechanical link between both engines via a drive shaft is crucial.
Further Notes:-
Study also the two Ch**y CERV Duntov prototype 4WD race cars of the early 1960's. They used just one engine with a torque convertor at each end of the small or big-block V8, and ran two Powerglides..one a rwd front engined trans going clockwise, and one a Corvair anti-clockwise trans. It had a 2500 rpm torque converter at the back, and a 3500 rpm stall torque convertor at the front. This gave a front rear torque distribution for good balance, and there was no wind up because the torque converters had a degree of differential action.
Hope you sort it out.!!!