I understand your position. Proven knowledge does not come cheep - in time or money.
Youíre probably right on the power valving. While restoring my Z back in Sept. '01, I experimented with jets and power valves with sequence listed below base on spark plug readings, vacuum readings, etc. In short, less seamed to be better. With my engine set up, I get about 12" - 14" Hg, so experimenting with 105 appeared reasonable.
Primary - Jets: 68 to 72 back to 68, Power valves: 85 to 105 back to 85.
Seconday - Jets: 72 to 76 back to 72, Power valves: 65 to 85 back to 65.
In the book, Holley Carburetor Manual by Haynes, Ch. 9 Reference and Specification, for the Model 4150 780, it list 72 jets for primary, 76ís for secondary, and power valves 105 primary, 85 secondary. Yet the 1969 Chevrolet Chassis Service Manual, p. 11 in specifications for the Holley carb (for 302's) list jets 68 primary, 76 secondary.
All spec's are in the same ball park but must assume they are set more for emission compliance rather than optimum performance?
As other have noted, the 72P/76S jet combination appears to be the ticket but again, I wonder what power valve combinations, etc. are being used?
I suppose that I try the 72P/76S jets with the 85P/65S power valve combonation next.