c30 starter, clunks when I turn key

[Dimebagdavesc30]

I have A 1972 Chevy C30 dump truck without the bed but still have the dump mechanicals. plan is for a flat bed that dumps with tool boxes on both sides. Problem is when I got the truck home and tried to start it all I hear was clunk. So I thought I need a new starter. So with new starter in hand I realize it just doesn't quite line up and is hard to even get it to set in right. So after a little filing to the part that hits the block I get it to bolt up. Start it and all I hear is clunk ever time. I think the starter gear is hitting the flywheel. it's a 350 with both block and trans housing mount. the block mounts don't even come close. I really need this truck to start but can't get the starter to start the truck. I would just love some Ideals as I am not a mechanic and am stumped.....mahalo for any and all help. 72' C30 dually