When I did my swap on my 70 F-250 I used a flywheel from a 1970 360 FE for my internally balanced 460. I used a starter from a 1985 F-250 460. I had to shim my starter to compensate for the 3/8'' spacer plate that I built to put between the engine block and bellhousing. I would say you either have a mismatched ring gear/starter problem or a starter clearance problem. To fix the clearance problem just use some washers to shim the starter to figure out how much distance is needed, then I would recommend getting a proper shim built from sheet steel by a machine shop or do it yourself like I did with a plasma cutter.