People worry too much about starting a freshly rebuilt engine. Inevitably there will be some wear (a cold engine is where most of the wear really takes place, after all). The trick is not to let the engine labour at low revs. Far better to get the revs up to around 2000-2500rpm and get that oil splashing around. If the bike has been standing for a while, I'd take the top end off and would directly lubricate the valves. I'd probably squirt some oil down the bores too and would leave it for a couple of hours to drain past the rings before starting. Then just fire it up and accept the wear as part of the natural life of the engine. The next most important thing is to keep that engine in service, which means running it as often as possible and always letting it warm thoroughly. Just remember to keep the revs up a little, and then run in the bike carefully by using all the gears and varying the revs; never too high, and never too long at any fixed revolutions. Sorry if I'm telling you the obvious.
