My 2008 MINI incurred very loud ratcheting noises, poor running, stalled, all within about 1 minute. I'm comfortable with mechanical work but oblivious to MINI's.

I've spent some time on the forum, what am I missing - are there any other high things to replace while it's apart (besides the clutch):
A. check for bent valves
B. get a bentley manual
C. replace timing chain with kit from one of the well known suppliers/vendors
D. Or replace/rebuild heads/block

How about the thermostat housing?

I think the R56 non-turbo has a vacuum pump right?
Vacuum pump was replaced 2 years ago - I'll check it's condition and for clogged oil ports?

 

Bentley manual is good. Also look at https://www.newtis.info/tisv2/a/en/ for repair procedures, torque settings, and special tools. Then use https://www.realoem.com/bmw/enUS/select for illustrated parts lists. You'll need the last seven characters of your VIN to get the proper data.

Chances are you have broken chain guides. It's an easy task to pull the valve cover and inspect. Post some pics for us?

T'stat housing change should be accompanied with a plastic hose change at the same time --- the one between the pump and housing.

And yes, your N12 has a vac pump --- they're also used for the power brake vacuum. That's the extremely fragile plastic hose connection.

Have fun, it's gonna be a real learning experience.