Nice looking truck. I think (hope) you are on the right track with the flex plate. They can be very noisy. The oil pan removal is a chore but glad you got it off. I'm not sure how to proceed after replacing the flex plate though. It would be terrible to replace it and find you still have a knock. Did you pull the main caps and check the bearings for wear? Maybe some of the engine builders can weigh in on a way to check out the rotating assembly without disassembly. Good luck with it.

Y's guys rule!
Looking for McCullouch VS57 brackets and parts. Also looking for 28 Chrysler series 72 parts. And early Hemi parts.

MoonShadow, 292 w/McCulloch, 28 Chrysler Roadster, 354 Hemi)
Manchester, New Hampshire