2.0 Zetec Silvertop with a 1.8 (silvertop zetec) sump and pick up pipe. Ensure the 2.0 has the manual CPS holder (not auto!). Mate to a BC 5 speed, or non-cable 5 speed ib5 (Escort mk6/KA etc)

130bhp with zero mods. Throw some cams and a decent manifold/exhaust at it to boot and its plenty in a Mk3 Fiesta to start. I did the above in an SI (mk3.5 essentially) for a mate (was 1.6 zetec) and it was great fun! Took me just over half a day and that included removing all the original gear.