Back in my airhead days i rebuilt my 100/7, buying my parts from don wilson who was THE bmw guru in nsw. I left him with the heads for new guides to be fitted and importantly, reamed to fit the old but still good valves, valve/seat facing, con rod small end line reaming etc. He was a great bloke to deal with and was was quite up front in telling me that all his machining work was forwarded on to Duncan Foster Engine Reconditioning at blacktown. This was 1984, don is long retired and sold his business which is now Motohansa, and yes you heard right , the owner is quite adept at making your money his. Oh, Duncan Foster are now in two locations and that leaves me wondering where "Motopansya" send their machining work to (and whack on a FAT margin)? All the best with your rebuild.