I wouldn't rule out anything at this point. There are some basic rules to troubleshooting that can help. I wish I used them more often.
1) don't rule something out assuming it is okay without verifying it first. This can lead to lots of time and $$$ chasing your tail.
2) check both the obvious and the easy things first. Swapping a carb or ECU or distributor for a known good unit is relatively easy (assuming you can borrow one).
3) make sure the basics are right ie timing, float levels, grounds, connections. I've pissed away $$$ and time on the float level issue.
4) use diagnostic tools where possible to gather real info ie timing lights, pressure gages
I'm sure there are more! As an example, my friend bought a pickup truck for cheap because it ran horribly. The air cleaner was badly plugged.