Lifter noise is due to lifters out of adjustment, on the too loose
side. Backfiring, if it's lifter related -- which it rarely is (it's
usually timing) -- is due to lifters too tight. So these problems
could be completely unrelated.

Valvetrain noise can also be due to bad geometry and other interference
problems.

Anyway, before going too far down the road of worthless Internet
speculation/advice, what engine is this? Is the cam hydraulic or
mechinical?

180 Out