Disappointed with my engine

I have a .040 over 360. Has **** J heads with 1.94 valves KB 190 pistons (small domes ). I have a Vertex mag, M1 intake and currently a 870 street advenger which is a vac secondary deal (carb needs further tuning). I have a Comp Cams Xe280r camshaft - I.570 242@ .050 and E .576 248 @ .050 installed straight up. Revs happily I've seen 7,000 on the tell tale. I have an 8" Turbo Action converter that flashes up toward 5000 and 4.33 gears. Car is very very light 1500lbs and it runs 6.3 on the 1/8 so that tells me it's only making 300 hp WTF ? I would think it should run well into.the 5's. What have I missed?