So here is the thing,

I have a 70's Chevy truck with the beloved 350small block. However it's been giving me some hard times. To begin with it had some valve bank (not quite sure if that's the official term, but as accelerating you would hear crackling noise) and when heated it got worse. Long story short after over heating it sat on the side f the road for a few hours, it now misfires on two cylinders. I plan a engine overhaul but before I start do you have any suggestions of what might be causing the two problems? The misfiring and Valve crackling?

Thanks!

p.s. I changed the spark plugs and wires not 300miles ago.