As the Ford based SS and RV have a basic chassis it is open to easy modification so why not fit the whole of a Subaru running gear onto it. it has been done using Ford Sierra 4x4 in this car, Intergalactic Crusader. Unfortunately the warehouse roof feel in onto it and I think it has been parted out.
One could start with a bare Eagle/Ford chassis or make one (following Eureka owning Bushboys, euro-nova forum) that follows the footprint but 2 1/2" wider down the sides with a vertical flange on top, cut the horizontal flange off of the tub and bolt it though the side wall giving extra seat room. Strip out all mounting points and offer up the complete Scooby sub-frame engine and drive unit, then hack and weld and make supports to suit, same at rear, then one would need to plumb it all in and then plonk the body back on to see where you would need to change to tunnel to suit the transmission and gearshift lever etc.
Finally going to see my body shell the week after next. Have also got a Reliant Scimitar chassis. Now looking into the engine/transmission options. I have just changed my beach buggy to Subaru power and there is just no comparison to air cooled.
Has I am starting from the ground up I have a number of options.
Retro eg. 1600 crossflow
Modern eg Vauxhall red top or vetec.
Silly eg Rover V8.
Different eg Subaru 4x4
However as I have 2 usable toys this one can be a special and be heavily modified.
Going on the last 20 years experience, don't go much above 120 hp, the power to weight ratio would make it almost undrivable on the road, ask Jason, his V8 SS is restricted to Prescott and those SS and Nova pilots with 170hp+ have to be very careful, Did you know that in the Corsa B forum many of the guys prefer the C14SE 8V 'sport engine' to the 1.6 or 2L 16V, guess what I have, Of course if you build a chassis from scratch with decent suspension and weight distribution it is a whole different ball game.