Do a compression test on a few cylinders and find out what your cranking PSI is: http://www.summitracing.com/parts/ANM-CP7827/
Next i would get another starter. The one you have may work on the bench, but the stator windings have been compromised/damaged due to being shorted from overheating. Do not crank on the new starter as you will simply overheat the stator winding once again, short out a starter solenoid, or overheat the wiring just as this one shows.
Verify that the wiring to the new starter solenoid is correct with a decent 12V keyed ignition hot source.
Verify TDC and then verify your timing curve in order to make sure it is firing correctly.
Next i would question cam installation. Get a degree wheel and degree the cam. Writeups do exist on the forum and also on the internet to better help you out here if needed.
From here if everything checks out OK then the only other thing that comes to mind is a possible clearance issue with the motor just being reassembled.