2ltr coupe f2 engine is your best bet mate fits straight in except from one engine mount that needs moving and i think you can run it in the standard gearbox and produces about 165bhp something like that. not bad considering you can pick um up for 200 quid on ebay
the thing you must remember is that putting a bigger engine in that produces big power will bend your chassis simple so try not over doing it when deciding on what engine.
also you must remeber to uprate everything from breaks to wheels and tyres on your car as you need to be able to stop befor you can go fast