I don't remember the exact specs/time, but we did do an intentional break in on the engine and I seem to remember running it for 30 min at 2000. The guy that helped me rebuild the engine was an ex-GM mechanic and a hot-rodder.

Additional info:
- I went back and adjusted all valves. Did the GM instructions, while running engine, loosening to tap/noise and then doing 3/4 turn back tight. Did for all valves including the #8 cylinder that seems to be giving the noise. Still a bit of tapping, so it's not the rockers (not rollers btw)
- checked carefully the push rods and all are rotating at a normal rate it seems
- dried all the oil off of the back (exhaust) rocker for #8 cyl. and it didn't re-oil when started. This has to mean something...no oil even though push rod is turning?
- took push rods out of #8 and they look straight and normal to me.