Thanks for posting.
Gonkulator agreed particularly well with this one:
No Spacer Gonkulator says
Torq 490 at 3700 (98% of dyno)
Powr 452 at 5300 (101% of dyno)
W/ Spacer Gonkulator says
Torq 490 at 3800 (98% of dyno)
Powr 457 at 5400 (101% of dyno)
That is about as close as things ever get.
But as we've noted, the Gonkulator came in high (5% to 13% high) vs dyno for your recent 3.78 stroke dyno tests.
I do think the headers are a little big, maybe costing 10ftlb or so on the dyno but that doesnt account for most of it even if true.
I noticed too - whenever you run one of the traditional fave carbs (750dp or 735cj) the Gonk agrees pretty well. But when your dyno has a less-favored/less common carb on top (750 straight leg, or 3x2 autolite or late model 600vac) on top, the Gonk tends to come in high.
Do you ever do "carb shootouts" on the dyno, say on one of those milder 390s? I've found a great variance on the Gtech, not so much with carb CFM but with carb style and "number" - eg some 4100 auto 1.12's down as much as 7% vs. others, no obvious reason other than a poltergeist or something.
Still trying to sort out why the Gonk tends to agree w/your 445s but comes in high on those 390s!