Chris - if your pistons are significantly lighter than stock . . . then stock rods may well get you to 500 HP with a Turbo without strain.
I sent my stock 292 rods to Speed-o-motive in Covina CA
They reconditioned them, recentered the pin/crank bores and then matched them w/pins to my
pistons. Assembly weights are all withing 1/2 gram and are quite a bit lighter than stock.
If you have your heart set on custom alloy rods - they can supply them or point you to someone who can.
www.speedomotive.com