I just picked up a 71 f100 2X4, local truck, 1 owner, unmodified and unrestored original, pretty cool truck thats part of the history of the town where I live. Anyway I think its in really good shape for its age however, its got a slight rod or main bearing knock. I'm wondering if its really hard on the engine to run it with a little knock in it? I was thinking about changing the rod and main bearings in it but wondering if I can do this with the engine still in the truck. Has anybody ever done this before? Any tips? Any information would be appreciated. THANKS!