How do you know it isn't the distributor out of time? I'd be looking at that before I start pulling the front of the engine apart.
Had a CJ that I got cheap 'cause it ran so poorly. Would idle ok-ish, but like half the hp it should have. Any hill and I was down to 2nd gear. PO said his mechanic told him to change the carb. He wasn't going to spend the money.
So I went with it was the filthy neglected carb. Would backfire once thru the carb if the engine was up to temp when you turned it off.
Replaced the carb with really cheap auto zone carb. And then it would backfire thru carb when you let off the gas at a stoplight too. So, next cheap auto zone rebuilt carb. Same thing.
So I went back and started from the beginning.
All the spark plugs were soaked with huge carbon buildup. Checked the timing. Woah! Couldn't even find any Mark's with the light. Cranked the distributor a good 30-40 degrees to find any lines on the crank pulley. Got it dialed in and the thing ran great! Took a bit to blow all that carbon that had built up. Power galore! Able to fly up a hill like a jet!
Moral of the story...
Always start with the easy stuff first. If the distributor is that far off then it just might be that someone hooked the plug wires out of phase. I would never have thought an engine could run that far out of time, but the PO did for over a year. And who knows how long before him?