Wow, great numbers on the intake ports. Seems odd to me that the exhaust didn't do better, having the seat hang over the port isn't ideal, but the air is blowing out the port so I would not have thought it could hurt flow that much. Those exhaust ports look like they should flow like gang busters, then again I remember back in the day when a good aftermarket SBC head with a 2.02 intake valve was doing pretty good to get 230 cfm on the intake.
Just looked up the numbers on a set of Lingenfelter CNC ported LS7 heads, they are pretty similar, though the LS7 heads flow somewhat better everywhere under .700 lift. But this is comparing a well developed CNC ported casting to a first cast prototype fresh out of the mold, not really fair but it bodes well for the FE power head. Your exhaust ports do better at all points under .600 lift though, so even though they aren't as good as you would like they are better than the LS7.
Here are the numbers from Lingenfelters web page :
LPE CNC Ported LS7 Flow Specs
Intake valve lift / Exhaust valve lift
.200 - 174 cfm / .200 - 120 cfm
.300 - 256 cfm / .300 - 164 cfm
.400 - 312 cfm / .400 - 200 cfm
.500 - 352 cfm / .500 - 222 cfm
.600 - 384 cfm / .600 - 234 cfm
.650 - 395 cfm / .650 - 239 cfm
.690 - 396 cfm / .690 - 242 cfm
Intake runner size: 272 CC
Exhaust runner size: 90 CC
I also found this article,
https://www.hotrod.com/articles/hrdp-1203-7-top-ls7-heads/ its fairly sparse on specifics, but its a dyno comparison of several LS7 heads on a 13-1CR 495ci LS engine with a large hydraulic roller. The heads listed above were in the mix.
They made a spread of 763-810 HP between 7 different heads on the same short block.
I have a funny feeling that, given the somewhat similar specs of Jays dyno mule and this LS engine, that Jay sould have no trouble eclipsing the 800 HP mark on his 504, I hope there will bw an epic " guess the horsepower " thread in the near future.