I could have saved you a bunch of trial and error, buddy!

That blower when I had had ZERO problems pulling my 446" motor to 5600-5800, I usually shifted right at 5500 tho. Cam was a Crower 282/292 (232/242 @.050 if I remember right or a little bigger than a Comp 280) on a 112 in at 107. I ran the old 933 Hemi springs, heck I still got the 906 heads laying around somewhere! something like 130 seat and 310 over the nose, most people run the comp 986's (if i remember the # right) that are like 110 seat and 285 over the nose.

But I don't think running a 108 Lobe spread 509 would be the way I'd go, way too much overlap so your effective boost will be even lower. I know Landy didn't recommend it for the blower, I had one on my shelf. He recommended a Crane split pattern that was just slightly smaller than my Crower but he told me my choice would work great, and it did.

That blower for what it was (to me) was very impresssive, I was able to take a basically stock compression high 12 second 440 bottom end and add 100+ HP with a swap that took less than 1 1/2 hours to do start to finish. this was the late 80's , no truly affordable Heads back then (except maybe the Iron-1's). I only ran an 850 on it, Landy told me when I bought it to put a 950 on it.

The Team G, Gary (RIP 180) used to crack up whenever I talked about That Manifold not being able to fall out of a tree below about 4000 rpm.

The only difference I can think of and it should be unrelated? is that my combo was a 4 speed.

I guess you considered fuel pressure or a restriction? Last time I saw a motor inexplicably laying down it was pick-up corrosion limiting flow....my friend didn't want to believe me until I dropped his tank and showed him.