Enging started ticking after a backfire

[ApacheNick]

Truck is a 72 GM K-15, 350, SM 465

My truck started making a loud, inconsistent tick after a backfire the other day. It almost sounds like a bad lifter but it's only really noticeable when the engine is warm and under load. With it sitting idling it will tick for a while and then it goes away until you drive it for a few minutes.

Another thing is the passengers side leaves a sooty grey mark in the snow while the drivers side does not and the tick sounds like it is coming from the passengers side.

I don't know if it matters but it has a MSD distributer, headers and full dual exhaust, high rise intake and a vary worn out edelbrock carb. All of this was there when I bought it and I don't know what if anything else was done to it.

Any thoughts on this are super helpful as so far I've been told everything from a bent valve to a bad bearing in the transmission!