what type of fuel should I be running in my '69 b.b. 396/350 h.p. (around 50,000 original miles)??

It all depends on the dynamic compression (basically static compression, which is reduced due to overlap)

My car has a static compression of 9.75, but I don't know the dynamic compression. I am able to run 91 octane without any knocking. I broke it in on racing fuel, and then every time I got to 1/2 tank, I filled with 91 (or higher if I could find it at the pump) In addition, I carry a couple bottles of octane booster, in case I ever have a problem.

I talked to a guy at a show who made a tray to hold two 2-1/2 gal plastic cans of racing fuel in his trunk. He bumped his octane by pouring 1 can in with every fill up. I don't recommend that....I'm just not comfortable with gas in my trunk.

I would try hi test with some octane boost, and see what happens. back off on the boost over several tankfuls until it knocks, or you eliminate the boost from the mix.

Unreal:

I should have been more clear about my driving habits. (forgot who I was dealing with here!!) I just take it out every now and then on weekends and sometimes to shows. I just use pump gas only. (I agree... gas in my trunk on these So. Cal freeways. I'd be on "headline news" before I knew it) thanks!!

don't waiste your money or time with the off shelf octane boosters like 104 and what not...they do nothing. Kemco would be the additive to run (lead additive like you had in the 60's).
Dynamic compression goes out the window too (if you want to konw why you can check the chevelle forum about "DCR" and all the discussions). to keep it short and sweet: your motor will eventually see the static compression. Load factor (which includes gearing, converter and car weight) will play a big factor as well.
So to answer your question: with the 350hp version, use 93 octane to be safe.

Thanks a lot... IF I cant find 93 octane, which way should I go? a little higher or a lower... now you see what a novice I am about this! thanks.

if you are aksing will it run 89? hmmm probably so if you drop a few degrees of timing. If you are asking if you can only find 91 octane, then yes it'll run fine, but you might still have to supstrace 1 or 2 degrees of timing. You can also invest in some Kemco, which is a lead additive that truly raise the octane. The added cost per gallon is very minimal. Ignore the 104 octan booster you can find at the store...they raise your octane about 0.1...they are garbage. (google kemco and read on what it can raise the octane too)

thanks again. will check out Kemco.