You could also try putting the old Bendix on the new starter.

Rand

Just a suggestion but did you phisically check both starter motors to see if the bendixes ( pinion gear )
Has the same amount of teeth and is the same diameter.
Also have you tried to bypass the electrical system alltogether using jumper leads and a known
Fully charged battery going straight to the starter bypassing the solenoid ( remove positive battery cable from starter before doing this to eliminate the oddys electrical system alltogether)
Also have you tried using the pull start to put the ring gear in a different position, maybe you have a worn spot on the ring gear and the starter can not mesh properly
Also if you have the starter out at the moment bench test it and make sure the bendix is moving all the way out
Hope this helps
Danno

What was the end result here ??

So I finally figured it out, for some reason the starter was not grounding when mounted. still havent figured that part out, but put a designated ground wire on it and boom works great.

Thanks for letting us know.
This kind of stuff is important for future reference.

Although I have never had to use one, the aftermarket starters I have installed actually have a threaded hole in the body for such a purpose.

Rand