69 Chev 4x4 stepside Truck starting problems

I have a 69 Chev 4x4 stepside. I recently put another motor in it from another truck I had. From the moter I took out I used the original water pump harmonic balancer and flywheel and the starter. The truck was starting fine when I replaced the motor but had a cracked ring which promted the motor change. The problem I am having is it will start ok and I test drove it and went to restart and it makes an awful grinding sound and sounds like the motor is laboring to start but does. After a few attempts at this it finnaly doesn't even turn over, if I wait a few hours it grinds and whines but turns over very slow then all of a sudden starts?
I put togeather another starter I had laying around and seemed to start with no problems and drove came back and having the same problem.
Any advice is welcomed.
Thanks, Ross Hi:

OK....a couple of things could be going on here.

1) Your flywheel may be too close in conjuction with the starter bexdix gear. Check for proper alignment by using shims. Trial