The bore is already set and that is on the block. Your bore is a 4.065.
You mean your Combustion Chamber size to run an xx compression ratio?
If your going for big boost I'd do an Ls3 conversion.
Just my .2
01 Ws6, m6, ASC#618 of 1583,40k Miles,shortblock built by AES the rest built by me,Ls3 416,FAST 102, NW102,LPE Ls3 heads,LsR 243/259 .624 114+3 ,C5r T/c,all ARP'd,12-1 comp,morel L/b lifters,melling O/P, kooks 2" headers,FTP 104mm lid,JAAM RamAir Kit,PB 10% UDP,UMI K-member,UMI T/A relocator,UMI SFC's, UMI upper and lower c/a,SLP T/A,UMI LCA's,UMI adj. PHB,Racetronix f/p,sjm abs delete,katech tensioner, dhm dual cutouts,magnaflow CB,Koni adj shocks,BMR springs,Moser 9in w/35 spline axles,4.11's and spooled, viperized T56,tuned @Straightline's mustang dyno 545hp/524tq