Help with rough running engine

[RedRider]

1970 C-10 w/ a 350 small block that has been sitting for 10+ years. Fires up just fine but idle and acceleration are very rough, like it’s not firing on all eight.

When I brought it home last fall:
Changed oil and filter
Squirted Mystery oil into cylinders and over valvetrain
New plugs/wires
Dumped old fuel, new inline filter.

At that point it started and ran briefly, just wanted to make sure it wasn’t seized or dead on arrival.

Fast forward to now, I’ve come full circle ready to revisit the engine. This issue was first noticed when I added a new intake (Edelbrock) and carb (Demon). It sounded like a dead cylinder so I checked compression (135-140 psi all around). I installed a new HEI distributor too (set at 8 degrees) but that didn’t solve the problem. There’s some white smoke out the tailpipe but I suspect that’s the Marvels oil burning out of the cylinders.

At this point I’m not sure where to go next. It certainly seems like an ignition issue but the plugs, wires and distributor are all new. Maybe the carb, but it’s new too. I’d appreciate any troubleshooting suggestions or maybe a second set of eyes to see if I’m missing something.