One of the main problems with fitting a ST170 (MT285) gearbox is that it's 'drive' dimensions are fairly unique and therefore 'special parts' are not too available on this side of the pond.
Standard ST170 parts (flywheel, clutch, starter etc) bolt straight onto a Zetec-E engine with the starter at the upper rear of the block, but......The flywheel is a quite heavy DMF and the clutch plate has a solid (unsprung centre). Operation is a concentric hydraulic cylinder. The splines of the input shaft are a Getrag, not Ford standard. Gear selection is by a dual cable system. The driveshaft splines/seals/inner UJs are also different to BC/IB5/MTX.
The most available parts, as I said, have to be sourced from the USA. One thing to note though is that all their flywheels/clutches are 230mm. UK has 2 sizes, 230mm to mid 2003, 240mm after.
I fitted a complete
setup onto a Zetec-E in my Focus. For a flywheel I used a s/h alloy Fidenza. Its well known (well I didn't) that alloy flywheels are a bit light resulting in a lot of noise idling in neutral. A steel one is better. The only UK made one is by TTV. However I'm not sure if they ever sorted out a road clutch to fit.
With no 'shock absorber' in the flywheel, its best to have one in the clutch plate. The best source for clutches is the US, which is now quite expensive However, the MT285 was fitted in the Mini Cooper S (BMW) with a 215mm flywheel. Also the Opel/Getrag F28 gearbox has the same input shaft. So with some modification I was able to fit a Calibra Turbo clutch, which works quite well. Looking at Vauxhall specs, it should take the torque of most N/A engines.
The only other thing I can remember at the moment, is I didn't like the pre-load on the selection detents, which I found too heavy. Many people remove the external counter weight to reduce the inertia, but reduces the balance of the selector. I made up a new detent assembly with a lighter preload.
If there are any specific questions/clarification......