hey guys...thinking about switching out my heads with aluminum 64 cc heads...currently runnin factory 76cc heads on flatop pistons and .040 overbore....would be around 10:5?....

Flat top 350
general average:
76cc heads = 9:1
64cc heads = 10:1

64cc heads and a 0.100" dome piston = 11:1
64cc heads and a .250" dome piston = 12:1

Depending on valve reliefs, gasket thickness, deck height those general numbers can vary about .25 of a point.

But the numbers are close enough for the information given in your post.