zetec is a quite lightweight engine for it's power. i drive a focus 2.0, with only an improved exhaust manifold (from an st170), and it pulls great! focus is'nt a lightweight car, got the leather interior and all those stuff...
plus, you can find a zetec abouth anywhere. i'm not sure about the duratec, but the weight is roughly the same iirc. duratecs even come in 2.3 displacement, and that could be a torqey engine, but at both engines it's better to use an aftermarket ECU.
for both engines, you'll need something for the lack of powersteering on your car (the belt runs via the powersteering), maybe replace the alternator, and make or buy an exhaust manifold and a water rail.
lots of kitcars use zetec engines, so maybe you can search on the kitcar sites a bit? should not be to hard to find...
and abouth the cortina suspention, maybe you could find anything to fit from a capri or an escort mk1/2? could improve the handling a lot!