Imo, stage 6’s on an RB is asking for fitment issues with 5209’s.
The stage 6 ex ports are about 3/8” higher and 3/8” farther apart than oe heads.
Not flaming....... it just is what it is.
I crawled under a friend's RB E-body w/ E RPM heads and Hooker 5209s and saw why they weren't going to work "out of the box" on my 440 Challenger w/ Stage VI heads.
Ended up using the Hookers on the engine dyno, but 2" TTIs on the car so I wouldn't have to re-engineer them to work.
Indy SR/440-1 heads would be even worse, since they raise the exhaust port even higher than Stage VIs & Victors do.
