550-600 hp I wouldn't bother w/ a girdle. twocents
I had a .030" over 440 that made around 625 hp w/ just ARP main bolts and stock caps and it was fine. Caps were walking of course, but no problems. Put a lot of runs on that motor.
That motor later got freshened up w/ some upgrades that put it at the 700 hp level, but I ended up selling it before I ever put it down the track.

CHIP
'70 hemicuda, 575" Hemi, 727, Dana 60
'69 road runner, 440-6, 18 spline 4 speed, Dana 60
'71 Demon, 340, low gear 904, 8.75
'73 Chrysler New Yorker, 440, 727, 8.75
'90 Chevy 454SS Silverado, 476" BBC, TH400, 14 bolt
'06 GMC 2500HD LBZ Duramax