Your method of pouring the chambers and runners sounds correct and your computations for the cylinder volume looks good, but your results for the head gasket volume are flawed and I don't see where you've included the deck height (top of piston to top of block deck) unless that's what the 761 represents, which would mean you've added 23,1 cc's for deck.

Assuming the head gasket is a composition example, the compressed thickness would be somewhere around 0.040". Assuming the bore of the gasket is around 4.100", the computation would be as follows: .7854 x 4.1 x 4.1 x .04 x 16.387 = 8,65 cc's. Even if you were using a shim gasket of ....say....around 0.015" thickness, the volume would be 3,24 cc's.

As far as deck height, unless you specifically specified to your machine shop to zero deck the block the last time you had the block bored, I can assure you that the piston is down in the bore by at least 0.030" at top dead center. So, here we go: .7854 x 4.06 x 4.06 x .03 x 16.387 = 6,36 cc's.

I'm assuming flat-top pistons which would have about 7 cc's of valve relief volume.

cylinder 738,28
chamber 68
gasket 8,65
deck height 6,36
pistons 7
total 828,29

compressed (chamber, gasket, deck height, reliefs) 90,01

828,29 / 90,01 = 9.202:1

Anyway, back to your needs.
More cubic inches and/or longer stroke will give you more torque. You're limited on changing the compression ratio to make the motor more efficient by the quality of available pump gas, so you will have to do it with displacement/stroke/camshaft.