Oh man, how embarrasing. (Uncle Tony/Nick's Garage)

I used a AMC type solid lifter with solid end pushrods in my 408 with no issues in 5 years. The AMC lifter isn't the problem here, it's an excuse.

The very first engine I rebuilt by myself was a 383 for my 71 Road Runner in 1981. I disassembled it and took it to the machine shop my Dad had used for years with instructions to hot tank everything, do a valve job, new cam bearings, hone the cylinders, polish and mic the crank and order the correct bearings, rings and a gasket set. I didn't own or know how to use a mic at the time and didn't plastic gauge it because the machine shop was supposed to have ordered all the right parts. Anyway I assembled and installed the engine, it started right up and sounded good until it warmed up. It was knocking in the front, back and both sides. After pulling the engine and disassembling it I discovered it was .010" on the rods and .020" on the mains, all the bearings were standard. The machine shop took care of it, polished and miced another crank provided the correct bearings and another gasket set.

I learned a valuable lesson on my first engine, measure everything and don't assume anything.