This is a been there done that thing for me. I picked up a 203,000 mile 72 145 with no rust that "had an engine noise" for free. It turned out to be a bad fibre gear but I wanted to see if it was worth fixing so I ordered the gear & was in a big hurry to see if it ran-air gun-snap-O sh__. I drilled a hole in the broken piece& the cam,tapped it,& loctited it. Ground off most of the bolt end for clearence & voila!it runs ........on 3 cyls. Bad injector[b20f-d-jetronic],bad intake gasket,& yes I knocked out the rear cam plug. It's run now for 4000 miles; Lots of other issues though. Resurrection is so expensive,but once you spring for the wheels & tires you're hooked! Happy trails. Mike M.