a lot of guys think they are 68 cc and early 340's were 10.5:1 but i've never seen one.
If you cut those heads to 65 or 68 cc ( i can't remember) then you would be at the factory 10.5:1 rating and be NRA legal.
I am pretty sure it is the 65 cc for NHRA and 10.5. I've worked out the numbers before.... lessee....yep... 66 cc does it with 5 cc eyebrows and 1 cc in the crevice area.