E30 M3 will be getting on a bit and will need shed loads spending on it to get 250bhp.
944 lump is very well engineered and is about the largest four cylinder you can get.
Can't recommend anything new other than confirm whats been suggested.
Unless this tickles your fancy :-D
http://www.wilcoxengines.demon.co.uk/cosy.yb.htm
Enjoy....