What fuel additive to use for a stock 429 4-V? What's a good brand/solution?

[Mr. 429]

My new (old) 1970 LTD has a smokin' 429 4-V in it.

I drove it about 70 miles from where I bought it to my house with about 1/2 a tank of year old, low octane unleaded plus approx. 7 gallons of 91 octane added to it just before the drive. It was running rougher when I got it home.

When I fill this tank back up w/91 or 92 octane what else do I need to add to it to keep it running smooth and safe, even when I want to get into it a bit? It is rated @ 10.5:1 compression, and the owner's manual recommends 99 octane fuel. Most additives only add 3-4 octane points at most.

Should I worry about falling short of this recommendation on a regular basis when I fill up with an additive? Do these add lead as well, or is that a separate additive?

I plan on draining the old gas out, and pushing the remaining gas out with air. Do I need to prime the lines with gas again when I fill it up, or will the pump do it automatically? Will it hurt the fuel pump?

Your advice is much appreciated. I posted a link to photos of my car in the LTD section. It needs other work, but the drivetrain is great.

Sorry for the long post, any advice is appreciated!