Edit: AGC worked!! Thank you man! it had slipped me...much appreciated. gonna try flashing tomorrow again, not sure if it will work with that subsystem ID tho
--
On high Sierra it works on base system without any patch with stock vbios. I just don't have boot screen, bright control, but I have image. so no need for patching to make it work, I resetted pram many times over with it like this and no change in behavior, still gives me video.
So I don't think it's the PRAM issue (I might be wrong, tho) , I think it's more the subsystem ID version mismatch between the 2 vbios roms.
problem is when I try to use patched OS systems, Dosdude1’s Catalina Patcher gives me black screen all the way through, but it shows image with the old crappy AMD card. so the system is installed, but neither stock vbios or patched vbios give me video output.
I'll give the AGC a go now
the patched usb installer also doesn't load the video drivers for Nvidia in either Catalina Patcher, neither Mojave patcher, only black screen.
I'm not using opencore, nor I intend to with this machine, because it goes to a friend of mine that can't troubleshoot it later. Also, I'm lost in the step-by-step for opencore, couldn't do it properly, even after days researching and reading countless pages here (and elsewhere), people write for those who know it already, so the learning curve is steep.
I flashed the vbios via linux (which is what I wanted) but no video, then I restored the stock vbios and had video again, but no niceties.