What's your valve notch cc? What shape is your piston head?

Here's my calculation: 505 / 8 = 63.125,
63.125 / 61 x 1000 = 1035 cc swept volume per cylinder.
To get volume above the piston for compression ratio r, divide swept volume by (r-1) so to get 11:1 compression you'd divide 1035 by 10 = 103.5 cc above the piston.
You say cylinder head is 74cc. Assume a 5cc valve notch and 2.5 cc in the 0.010" space above the piston, plus a 12cc head gasket. You have 93.5cc.
You need another 10cc to get down to 11:1.
Completing the calculation:
If your piston is flat top with just the 5cc notch, your true compression ratio with the 0.040" 12cc head gasket is 12.07:1.

E85, anyone?

R.