Engine sizes...
 

I can't remember right but do only 1.7 liter T4 engines mate directly to the T1 bellhousing? If this is the case, how hard is it to adapt a 1.8 or 2.0 liter? Making engine selection soon, any info would help.

i believe it is just a matter of using the right size flywheel

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They do all fit, only the flywheel choice is a bit difficult, take a look in the 228mm thread.