I used to do the all in porting, polishing, bowl cleanup, flow matching on my 7000+ rpm SBC race engines. They made huge power gains through the entire rpm range and way higher power at the top of the range over non-preped heads.
Just my opinion, save your money on the high flow heads. No doubt there are some power gains to be had, but the rpm’s you’ll be operating at most of the time, I personally don’t see the ROI.
That xr270 cam, 36# injectors, headers, and tune has me pulling a camper trailer in 4th gear through the mountains with throttle to spare. I’ve got 5:13 gears which puts me in the middle of the power curve at 70 mph and when I want to pass unloaded on the highway in 5th gear it will still take off when needed.
just my experience though.