Haven't done much to the Belair yet. Still installing seat belts - much more difficult than I expected, but making progress when I actually do work on it. Ordered new rubber w/ steel insert valve cover gaskets and a smaller breather to temporarily fix a clearance issue with the wiper motor.
I decided it needs a 5 speed. 4th gear and 2700 rpm at highway speeds just isn't for me. Especially when almost no one limits themselves to highway speeds any more. The tkx Karl suggested is pricey, but will make it more enjoyable to drive.
As for the engine, I think I'm going retro-resto-mod. It has a 350 that seems strong enough and seems healthy so I can't justify to myself to do a complete swap yet. But I came across a reasonable deal on an old Tuned Port Injection system. Yes, there are much better systems available. But TPI was all the rage in my formative teenage hot rod years. And it's still hard to beat the eye appeal w/o going to a 6-71 through the hood. FiTech makes a standalone ECU system for the TPI now that at least gets the tuning up to modern standards. You can't make great hp with TPI since they don't breath well above 5500 rpm, but it's a street car and there won't be much time above 5500 rpm. And the bottom end torque of the TPI is impressive.
If there's interest, I'll document the changes here. This forum is still a great place for sharing of info and ideas in spite of the recent rise of a Goblin antagonist.