I went back and re-read your initial post on this thread. As I understand, you bought a used, complete 454 from a 'reputable marine dealer'. If he is indeed reputable, we would have to assume that he knew some history of that engine, and that he had heard it run, if not even run it in the PO's boat before it was pulled. Bottom line, it would be reasonable to assume that it ran fine when he sold it to you.

You then decided to "upgrade" to a larger, but rebuilt 850cfm carb to replace the 650 that it had. Since then you've had problems with hard starts and rough idle. Instead of going into the guts of that engine isn't it logical that your problems lie with that replacement carb? Was it a factory rebuilt unit, essentially new in the box or did you get it from someone who "rebuilt" it, or maybe you rebuilt it yourself? Regardless, I think that it's a pretty good bet that you've got a carburetor problem, but now you're chasing changes on multiple fronts so it's going to be harder to sort out all of the gremlins. If it were mine I think I would reset the timing as close to where it was when you started (hopefully you put a reference mark on it before moving the distributor?), drop the 650 carb back in place, be sure you have good, clean gas (no fuel filter plugged, no water, not stale) and see what it does that way. You may just have one weak cylinder, and it may run OK, but not optimally if you run the gremlins out of there.

Good luck with it. Boats have their own set of issues that a lot of us have not dealt with.