The options you have are:
1.6 zetec se from a zetecs
puma 1.7 (most popular)
2.0 zetec (turbo)
2.0 I4 from an rs2000 16 valve
None of them are that hard to do, for simplicity, go for the puma, can be done for about 300 quid, for ultimate power, go the 2.0 zetec turbo route.
Now lets see some pics of the car (mk4 owner here!)
I'm putting pics on wen I've got the kit on do u know anyone hu can put a puma lump in