@codyNC90 Re: VRAM for the 5xx, start a new thread in Hacks to avoid tangential overload in this thread.
LCD resolution seems a much stickier wicket than external output. Same deal with the 2300c and everything in between.
I've always suspected a firmware limitation, but it might be possible if only a control panel hack is possible. IIRC the ASICs involved, someone transplanted SCSC(?) from the 1400 into the 2300c replacing CSC(?) heading toward a solution to this limitation.
Check the 5xx DevNote against 2300c and 1400 docs to see if the Video Controller ASIC, matches. That'd be where I'd start. If that matches, then determine the VRAM IC package and look for a higher capacity IC in the same footprint. If that's no go, they're is always the chip stacking gambit as a last resort, cubic and signal allowing of course.
I haven't looked at this in many, many years, but it may be worth taking a shot at it again. Look into the 190, 5500c/(ce) and 2300c at the same time. The prospect of pulling this off across those generations might catch the attention of the amazing enlistment of current generation hacking magicians.
Again, start a dedicated thread in hacks and link to this one, it's a bit off topic here.