Plenty to choose from, the puma is the easiest one to do (pretty much a straight swap), also the 2.0 zetec goes in pretty easily, as does the I4 RS2000 16 valve engine, to be honest anything will fit with a bit of work. Personally I'd go puma as its straight forward, but if you want big power, go 2.0 zetec and turbo it. Plenty of info on this forum for you.