Slant runs like crap when first accelerating..

pull the distributor and take a look to see if the bushing, plastic gear or advance plate/weights have issues....then look at the ignition box if electronic.

After that, grab the crank dampener and turn it back and forth , feel for when the timing chain slack tightens up and grabs the timing gear, how much back and forth there is can tell it's time for a chain and gears.

The other thing that can happen is the flapper in the exhaust manifold likes to rust/crust up and stick closed, make sure it moves.......and after that ...lol ....look at the carb

Thats How I would do it.