Boyoboy, what a story! Never heard of timing chain tensioners held in place with oil pressure - as pointed out in another reply, on start-up there is virtually no oil pressure for a couple of engine revolutions, seems that not only 'older' engines would go out to lunch if that was the case. I'm not familiar with the internals of the M60 but in most engines the tensioner is a spring-loaded jobbie that keeps constant pressure on the chain, irrespective of oil pressure.
My guess is their apprentice took your car for a burn and blew it up ......
Ask to see your original engine.
Don't pay a penny for anything to do with the engine.
And I'd have to ask also, why new calipers? Phew!!!
June 88 535iA, 173,000 km; Sep 00 735i 170,000 km