I have to agree on a couple points here - and make one.
First is that the timing at 28 degrees - if that is real - is costing a ton of power in any normal vintage OE head's combustion chamber. As George noted, I would expect to see 36 or 38 total.
Next is the comment on valvetrain control. Also agree - it's pretty obvious that she's floating really badly over 6000. Kind of surprised the operator would take it up that far, since that should have been very audible. Cannot tell you whether the problem is a simple lack of spring pressure or if it's a system harmonic - but you MUST change something if you expect to run it that high or you WILL be breaking parts. As mentioned, you should see a fairly smooth roll off on power past peak.
I need to point out that a 950HP Holley is perfectly appropriate for this type of build. The 950HP is NOT 950 cfm. It is essentially an 850 base plate coupled with a 750 main body, and flows roughly 820-830 at SAE 1.5" drop. This combination was extremely popular with racers in the 80s/90s and Holley replicated it when the HP line was introduced. The whole 950 thing was entirely marketing driven, and is very misleading.