The worlds your limit, how about a 14 litre twin turbo V12 2 stroke diesel from a canadian forestry digger? 525 bhp and a whole loada torque 
If you put a big engine under the bonnet, itll handle like a pig because put simply the car was not ment to handle anything bigger than a 1.9 and no amount of suspension work or chassis welding will have the car the same as before.
If I wer you, I'd concentrate on getting a bare shell and work from there. See what fits with a gearbox, how much work will it need etc. I personally think 2.0 16v turbo should be big enof, 5 pot will fit but is a tight squeeze. Make it 4wd! Remember group b rally cars could run up to 1000+ bhp, often running 450 - 600 bhp normally, 0-60mph was 2 seconds on tarmac. And those engines were only 1.8 litres :devil:
If you put a big engine under the bonnet, itll handle like a pig because put simply the car was not ment to handle anything bigger than a 1.9 and no amount of suspension work or chassis welding will have the car the same as before.
If I wer you, I'd concentrate on getting a bare shell and work from there. See what fits with a gearbox, how much work will it need etc. I personally think 2.0 16v turbo should be big enof, 5 pot will fit but is a tight squeeze. Make it 4wd! Remember group b rally cars could run up to 1000+ bhp, often running 450 - 600 bhp normally, 0-60mph was 2 seconds on tarmac. And those engines were only 1.8 litres :devil: