Id go for a 2.0 zetec out of a early mondeo. Quick, easy readily avaliable engine! Pick them up for peanuts! Theres a few threads on here that show you how to fit a zetec!

You could go down the rs2000 route but there not so much of those engines about compared to the zetec and you will pay about 3-4 times as much for one but with 150 bhp well worth doing. I had a mk5 van with a rs2000 in 164bhp very fun!

Id go with the zetec tho if i was you!