best and easiest option would be a 2.0 zetec, they fitted the 1.6 and 1.8 zetec engines into mater mk3 fiestas, so it's really a pretty easy swap as long as you can source the parts. they're 130bhp as standard and can be tuned to make a load more depending on how extreme you want to go. they can be mated to the 4 speed, but you might as well pick up the matching 5 speed from something like a focus, as well as the cable shifter to give you a more modern, positive gearchange.