I've got a mk3 with a sigma in there and its an absolute gem. defo the way to go. forget about the old zetec is my recommendation!
not so hard to do.
A few things I had to do was to mate the bellhousing from the sigma to your mk4 box and that side of the mountings are then sorted. you then need to weld a support for the driver side engine mount and that's about it! My engine is standard running on emerald ECU and better exhaust manifold and