"Interesting" Problem...

[Vanlande]

Hi!

I'm new here, just picked up a '66 C10 SWB Stepside, good lookin' truck. Pretty much the only 60's era tuck I like, as i'm more of a car guy.
Brief history of me so you know where I'm coming from with the problem I'm having... Worked on Classics since I was in high school (got a 77 Pontiac Grand Prix when I was 16) so I have 8 or 9 years experience. Always had cars, some GM, some MOPAR, even a Ford and an AMC (67 Ambassador).

My new Chevy has (I think) a 77 or 78 Caddy 425ci bolted to a TH400. Guy i bought it from told me 500ci, but that ain't right. Here's how I found out...

Bought the truck running, hesitated on cranking but then fired and ran ok, pings when you stomp it, but if you go easy had some get up n' go. Then, about a week after I get it, that hesitation turned into grinding, got 1 last start out of it then drove it home. Looked under it, only to find a broken nose cone Then I look for a replacement for a 500ci starter, and it's a completely different thing! Turns out it's either a 472 or a 425. Got a new starter, bolted it on, appears to be too close to the flywheel. Shimmed it, as well as adjusted the timing. Started great for about 2 dozen times, now back to the horrid grinding sounds.

Gonna crawl back under her and see if the bolts came loose in the morning, and make sure I didn't break another nose cone. Any suggestions on what this could be, other than what I've covered? I would greatly appreciate it.