I am doing the same thing. I have a 98 Focus Estate with 210'000 miles on the clock.
I have a ST170 Gearbox sitting in the garage and Have been given a low milage 1.7 Puma engine. My thoughts are marring up the 6 speed box with the Puma lump and fitting it into my Estate..
What are the pitfalls?
What do I do about the VVT cam?
What else have i got to change.
The Brakes are already uprated along with the suspension.
Give me your Ideas,,,