1981 Chevy Van timing

Engine Mechanical problem
1981 Chevy Van V8 Two Wheel Drive Automatic

I have a 1981 Chevy van with a 305 motor-Vin# H & G
I put new chain and gears in a long with a new distributor
I set the dots-cam dot at bottom-crack at the top
I dropped the distributor in-making sure the rotor was pointing to # 6 on the cap
I put it all together tried to start it-It back fired through the exhaust
I did the same thing again as above-but this time-I turned it over till the crack was on compression
I dropped the distributor in on # 6-it back fired through the carb
I reversed the distributor 180 degrees-then I tried to start it-it started after moving the distributor back and forth
So I shut it off-two hours later I tried to start it-Nothing
Once again I pulled it all apart-Reset the gears-then I turned it over till the cam gear was on compression-(so I thought)
I dropped the distributor in-making sure the rotor was pointing to the 12 O-clock high-I tried to start it-Nothing
I repeated all the above several times-as well as dropping in the distributor & pointing the rotor to different points on the cap-
still it will not start-At this point in time-it is on compression-But I do not no where to drop the distributor in-where to
point the rotor-or where the cam gear should be set at.
I guess I could take off the exhaust manifold and watch the valve open as I turn it over-then when it's open
drop the distributor in with the rotor pointing to 12 o-clock-then bring # 1 piston up on compression & try to start it.
Any idea what else I can try.