Help Needed - '68 c20 w/ 396

[Rippin-J]

I've had my '68 now for over a year, and the guy I purchased it from "had the motor rebuilt" but then it sat parked in his shop for 5 years before I purchased it. It's never run great, but for the past 6 months or so is been SUPER rough, too sketchy to even rip around the block.

It'll turn over okay (after a jump..... alternator maybe?) and even idles OK for a few minutes. Once it warms up it begins to spit and sputter a bit, sometimes sounding like it's on the verge of dying. The left side (driver's side) seems to be the worse as it blows black smoke (not TONS) out of the pipe. Also, when I dump the throttle and throw open the carb, it is VERY late to respond and near dies.

First, the thought was carbs because the Quadrajunk that was on there wasn't even opening up with the throttle. Replaced it with a brand new Holley Street Avenger. That didn't fix it, but the motor gets more gas now.

The thought now is that the issue is something internal: compression, valves, gasket, piston (rings), etc etc. My major dilemma is that my network of 'gearhead' buddies are all in Colorado and I now live in Charlotte where no one in my network fiddles with or knows much about old cars. Oh, and I know very little about the diagnosis and repair of internal components.

So here's what I'm asking the forum for help on:

1) What novice level tests can I do to further diagnose the issues I am having.
2) Does anyone know anybody or is anyone in the great Charlotte area willing to help me learn the ropes.

It's a very clean truck and motor, so I'd hate to just scrap it and replace it with a rebuilt 350.... but am willing to if that seems like the best case scenario.

Anyways, you all have been very helpful in the past so I have no doubt that someone, somewhere will have some ideas.

Much appreciated,

Jordan