need skilled info
I know you said you don't want to replace your bottom end. But the chambers on the 781 heads are at least 118cc. So it would be nice to know if the pistons are flat top or domed. For an example KB pistons have three different size domes -12cc, -25.5cc and -43cc. With the 781 heads you would need a -12cc dome to have a 9.173 compression ratio which would be ideal with pump gas. The compression ratio with a flat top piston would be 8.233 a little on the low side.