Here is our Buick (Rover) 3.9 bored to 305 Chevy size. Forged Icon Pistons, 6" narrowed Scat rods. Mild cam. Best performance with stock Rover heads is 8.84 @ 150. With Wildcat heads we have yet to make a pass.
Nice car! I have always been a fan of racing with retro engines... non-chevrolet, specifically. It is a difficult thing to do well & it looks like you are doing it well. You have much to be proud of.