Boss head build. Need advice

Kasse B9 heads, D9 block. Going .030 over. This will be a pump gas, solid flat tappet build, Scat stroker kit.
So piston choice is -8 or -18 CC's and stroke choice is 4.3 or 4.5.
Will be cammed to run power brakes. I've never worked with so many CI. but probably less than 240 duration I figure.
So question is, what stroke and what piston?

i have a 557 with the kaase boss 9 heads and engine builder stated that compression is 11.6.i wanted to run it on pump gas but this maybe to much.has a kaase specd solid roller.
pistons are diamond flatops .had to cut deeper exh pockets for piston to valve clearance.so if yor are looking for pump gas that also depends on what cam you are going to run.
use an online comp ratio calculater.or best to call kaase and ask his guys for cam and piston recomendations.

Thanks for your reply, ordered a 545 kit with 19 cc pistons. Wallace caluctor says 10.65 compression.