I buzz mine to 7200ish and it was still making power, but my cam/valvetrain is setup for that. 8500 i cant even imagine and for me it isnt needed to do what I am after, but any of these t4 turbos will have hella backpressure at higher boost levels, another battle you will have.
A t6 may be better suited for your goals. After a certain hp #, or ET?
You can make 800rw on that 76 thru an auto, thats enuff to sneak into the 8s on the right car.