So 8:1 will make it pretty mellow compared to something higher, but I will tell you, I resurrected a build gone bad for a local guy.
Same 390, same 8:1 compression, fresh build. It's on the forum somewhere when I did it. Edel heads, RPM intake, 800 Edel carb, and FPA headers and a 279 adv Thumpr cam in a little 67 F100
It was not fast, LOL, but it ran surprisingly well even with lreal ow compression and it was far overcammed and too much intake. Even had a close ratio toploader in it until we swapped it for aan early TKO, similar to the TKO-500
I'd love to see you stroke that thing and make some compression and torque, but sometimes even a little one will surprise you.
I personally would return those rockers, listen to Brent, buy a set of aftermarket stands, cut them down and run stock hyd rockers. It'll be bullet proof. I am baffled on what it'll make for power, but the heads should let it hang in there, might want to consider an RPM intake to take advantage of them