Breaking in a rebuilt 351 Cleveland?
if has been started up at all recently, I don't think you would have to prime it, but I have been reading alot of stuff on using the GM EOS additive and Shell Rotella diesel oil to avoid destroying the cam.
I was told gentle break in, like 2,000 rpm for 15-20 minutes, and 500-1,000 miles of partial throttle driving. NO hammering it.
Asside from that, just check over stuff, check for leaks, etc.
Change the oil, and if you want, slice the filter open and inspect it.
1972 Torino GTS 351c 4v cj 4 speed
1973 Torino GTS-1979 F150 4x4