There are lots of hassles involved in this, main one being the n/s engine mount.
It can be done.
May be worth your while if serious about doing this to talk to skodaboy on the briskoda forum as he was looking into this and is a very clever chap, he has fitted a mk4 golf gti engine into a felicia, so knows his cars!
1400 16v's can be 75 or 100bhp, you could also go for the 1600 16v with 125bhp if youre going to be pulling it all apart anyway?