65 dart 225 rebuild.

I posted a few pictures of my slant 225 rebuild and was told just from the pictures that there was no way I could get 320 horspower from a SL6. One Person said at best I had about 7:1 and maybe 100 hp. Well can someone explain to me how thats possible, seeing that the factory specs for my engine was 8.4 and the max HP rating was 145. Are you guys saying that rebuilding a slant makes less HP? Just a few things that were done. Block decked 25k, head milled 110k, bored 40 over with flat top pistons. 3 angle VJ. Head ported polished. Balanced blueprinted, cam is erson 224 410. Weber 500 cfm 2bl carb with clifford intake and headers, roller rockers to be installed. Here are the factory specs from ALLPAR.COM
Engine 225 cubic inch
Carburetor Single barrel Single barrel
Bore and Stroke (nominal) 3.4 x 3.125 3.4 x 4.125
Bore spacing (CL to CL) 3.98 (1-2, 3-4, 5-6);
4.0 (2-3, 4-5) 3.98 (1-2, 3-4, 5-6);
4.0 (2-3, 4-5)
Firing Order 1-5-3-6-2-4 1-5-3-6-2-4
Compres. Ratio (nominal) 8.5 8.4
Cylinder Head Material Cast iron Cast iron
Cylinder Block Material Cast iron Cast iron
Cylinder Sleeve None None
Number of mtg. points (Front) Two Two
Number of mtg. points (Rear) One One
Engine Installation Angle Lateral 0°, Up 3° Lateral 0°, Up 3°
Taxable Horsepower 27.7 27.7
Publishing max. bhp* @eng. RPM 115@4400 145@4000
Publishing max. torque * (lb. ft. @RPM) 155@2400 215@2400
Weight (piston only ) oz. 16.4 16.4 So if these are factory specs how can my rebuild not have more than what this says? I will have it dyno tested to see where it stands. I will post results when this is done. I am not a engine builder but it seems to me that the head work alone will increase the HP by 50! With my understanding of how much it was milled and flat tops that puts it at 10:1.