Is the front bracket on the starter? It should be a metric bolt and the only place I have found them is at the dealer. Make sure you didn't break the block when the bolts broke and that the starter is shimmed right.
I believe I may have resolved the problem. Those of you who are familar with the 93 6.5L know that there is no tolerence for the starter nose in reference to the bell housing. What I believe to be the cause of the problem is the starter nose was a little too long. When I got the first replacement starter from napa it was a no go ( bendix locked in flywheel). As we started to diagnose the problem we noticed that the starter was floating if you will, pulled and pushed on back of starter and it was not solid. Starter appeared to be the same as the one we removed. We took the starter back to napa and explained what we thought was the problem. they replaced the starter with a different starter that appeared to be 3/8 - '1/2 in shorter. works like a charm. when I inquired what the differece was between the two as usual no comment. sorry. As for shimmimg my undestanding is that you do not shim these starters. Again could be wrong.
Well after i bought my truck, my starter stopped hitting, i found that one of the bolts had snapped, so i had to dig the bolt out and put two new ones in, I think that the last person to put the starter in didn't use the right torque specs, so make sure if that is the problem don't over tighten the bolts