Did you prime the oil pump? If not, before you start spinning the starter, remove the oil pan and remove the cap holding the oil pressure relief valve. with no sparkplugs in the engine, crank it over a few times with the kicker and the oil tank full. Once oil starts flowing from the relief port, button everything back up on the bottom of the motor and remove the oil gallery plug (where your pressure gauge is. Hand kick it a few more times until you see oil appear. After replacing the gauge a few more hand kicks should have all the galleries filled. Also, remove one of the tappet covers and pour some oil in there. This will go to the sump and help prime the pump for the oil return.
I went through this on a motor I just redid. Cranked and cranked and cranked, nothing. Did what I just described and I had oil pressure in no time.
i know i am reviving an older post but i found this very helpful, i finally started my bike for the first time ever since ive owned it and since i rebuilt the top end. i followed hondamans book and primed the oil pump beforehand. i used a big ol syringe type injector like we use at work and poured about 4= oz in the head and probably about 10oz in the gallery port and kicked and cranked it until oil started pouring from the gallery then put my direct reading gauge on and kicked a few more times until i saw about 10+ PSI and then put my plug back, and hit the started almost immediately my oil light went out and my gauge read 20PSI
i am running 20w-50 castrol and once its started i read about 70 PSI on the gauge
but i wanted to give a big thanks to the guys on this thread because i was nervous i know how critical oil pressure is and i didnt want to kill my motor on day 1 this made life sooo easy!
That's OK....Andy is still trying to build oil pressure in that engine. 
That engine is a work of art and a joy to ride now that its been round the block a few times
