Very good then. Yes, a replacement Holley carb for that engine WOULD run a significant fraction of their EFI system, enticing consumers to purchase the latter, by design. Well since you've committed to it, you certainly will do best to run 91 octane with perhaps a splash of good 2-cycle oil to supplement. According to my 1968 Parts Catalog:
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The furthest right column corresponds to ALL 440 engines listed for 1968, and shows the head #2843904. I don't entirely trust this source, despite it's copyright date and such, as I've seen 440s with both 906 and 915 heads on fairly virginal 1968 B/RB engines. I suggest removing a valve cover and looking at what the factory bolted onto your block when they built it. Empiric FACT always outweighs epistolary references in my Book.
Regardless of what you find, there's an excellent probability that the valve seats will be in pretty decent condition, based on what you've related about the car so far. The Happy News for you comes now: provided you don't ABUSE this excellent find, your valve seats should be good for many tens of thousands of miles yet with that EFI system, even sans hardening or hardened inserts! I type this based on what I purchased for my own family ride, which now has been in daily use for 4 years. The valve seats on the pair of 915s I obtained were in decent condition, but I ordered hardened inserts for them just to insure that they would serve well for a long time to come. We don't have lucre to waste on whimsical head and valve jobs in our household; once should do for these for a good long time!