351C idling funny

My 1st suspect would be the 2 year old (or better) fuel you're attempting to burn.
If you have 1/2 a tank or less cut it with 5 or more gallons of premium fuel (or a 108+ octane fuel) and run it all out. Then change the fuel filter(s) and re-fill with the grade you normally run. or..... just drain the tank and put fresh stuff in. It's just harder to "leagally" dispose (not on your weeds like i do) of the old fuel that why 1st suggested cutting it with hi-grade stuff.

Yeah it could be. With 11:1 you have to run premium fuel at bare minium and actually probably toss some 108 additive in for good measure. But it all really depends on your altitude and how your engine is built. I've seen cast iron headded 11:1 engines run on 87 octane when i lived in Albuquerque, NM. Blew my mind, me originally being from a sea-level town seeing that.
Here our premium is 92 octane and there are a few places in Portland that'll sell 108 and 110 out of the pump. I buy 110 trick for my Tunnel Ram car in 5 gal cans and cut it with 92 octane pump stuff. Seems to do the trick and doesn't break my wallet nearly as bad.

I'd comb the engine for vacuum leaks too. Never know of you bumped a line off or if some rubber dried up and split causing a vac. leak.

Haven't really ran an MSD setup yet. I normally run those Pertronix units that replace points.... man, night and day difference. I also use Mallory Promaster coils with that pertronix unit.