Lead Additive? Octane?

[CriticalMass]

Using search I see this topic has been beaten to death, but none of the threads quite answered my question, so:

My father passed away and I'm left trying to maintain his ERA 427SC (feel like I'm going to have to give this background every time I post since otherwise you would wonder my I can't take care of my own damn car )

There was a time (when pump gas was 89 cents/gal) when he ran his car on leaded racing fuel. I don't remember the octane rating but it was somewhere around 110. Other times he used pump gas with a lead additive/substitute. The problem is that I don't know exactly what he was running it on when he passed away.

There is a 99% chance that its pump gas...but I can't be sure if he was using a lead additive/subsitute and/or octane booster.

My question is without knowing the compression ratio of the engine can I just go to the pump and get premium (91/93 octane) and be relatively safe that it wont need retuning? Should I use a lead additive/substitute? Should I also use an octane booster or mix pump gas with racing fuel? Or is solving this problem going to require figuring out the compression ratio?

Essentially I won't use any octane below 93. So if I happen to put in fuel of higher octane than it's used to will it cause any problems? If so, what needs to be adjusted.

If you suggest any additives and you have recommendations of brand names I would appreciate it...I've never had to run a car on high octane fuel.

Thanks.