I'd be concerned about the end gap on the oil rings. The expander may not be in right or the thin rings not sitting right ? I also go thru and check out the starters,alt. or gen.,water pumps & radiators on any engine job I do because the engine is going to crank harder and run hotter then when worn out.
I can't say as I have ever had trouble starting a fresh rebuilt engine. I crank them up without spark plugs or injectors to get oil pressure first too. Also use engine assy. lube on them when going together.