undecided on engine choice

[gundog]

hello all.
whilst waiting for my chassis to arrive im starting to think about which engine to fit.i really like the idea of a bike engine or a zetec 2.0l.i dont have a donor car as mentioned before,so all options are viable as ive got to get an engine anyway.
if i get a bike engine how hard is it to make a paddle shift?does any one have any plans or details on how to make my own?
im only thinking out loud here so all advise will be gratfully accepted.

andy