Dissapointing performance

I bought IMMS rhs heads to my 360 and after swap I didnt see any performance gain. My old heads were badly ported 596 heads with 2.02 inch valves. They had clearly too small pocket porting area compared to valve thats why I thought that they are badly ported.

I tried 35 and 33 ignition advance and I didnt see difference. Car can hardly do a burnout. I did try 1/8 mile run after and before head swap and I gained 1.8 miles per hour trap speed! It was 85 with these new RHS heads. Putting weight and that speed in calculator I got 305 horsepower. Thats nothing I feel I should have more like 400hp than 300. I am very badly dissapointed to these heads. Can anyone quess what is wrong in this engine?

Here is my combo

360 0.040 oversize
Kb107 pistons
10:1 compression ratio (yes I measured it)
piston to head distange about 0.078 inch
Comp cams mechanical flat tapped 282 degree cam in advertised duration 240 in 0.050 lift. LSA 110 ( I did degree cam it is right )
RPM intake
600 edelbrock vacuum secondaries
1 5/8 shorty headers
2" dual exhaust (might be little small but not that small?)

20 decree idle ignition advance and 35 total. Car runs and feel right but only doesnt have power more than it has.