Hi Waglo,
At this point, I highly recommend you to upgrade to the new version of GM. The reason is that the monitor_specs format has been extended (now it's crt_range#) with two extra values that are going to help you a lot for creating individual ranges. Please remind these are NOT modelines, a modeline looks like this:
Modeline "640x480_60,0Hz 15,7KHz (60Hz)" 12.324 640 648 706 784 480 483 489 524 interlace -hsync -vsync
On the other hand, monitor_specs (now crt_range) lines are like a set of requirements that any modeline must meet.
Now, the new values are used for defining vertical resolution ranges, so you can specify different settings by vertical resolution groups, like this:
crt_range0 15700-16200, 50-62, 1.098, 3.293, 6.587, 0.064, 0.160, 0.550, 0, 0, 192, 248, 0, 0
crt_range1 15700-16200, 50-62, 1.098, 3.293, 6.587, 0.064, 0.160, 0.550, 0, 0, 249, 256, 0, 0
crt_range2 20500-21000, 50-62, 0.782, 4.693, 4.693, 0.986, 0.148, 1.380, 0, 0, 257, 288, 0, 0
crt_range3 22000-22500, 50-62, 0.782, 4.693, 4.693, 0.986, 0.148, 1.380, 0, 0, 289, 320, 0, 0
Of course you'll need to grab the right values for each range from Arcade_OSD, as you've been doing, it's just that now you have more power to send each resolution through the right crt_range line. This is the most important feature of the new patch.
So here, crt_range3 would represent the vertical games with resolution of 289 to 320 pixels, rotated. The horizontal frequencies are guessed, it's quite a straight forward calculation, and you can gather them too from Arcade_OSD.
There's a problem though. VMMaker is not up to date with GM, I need to find some time to do that. So it won't accept the new crt_range format. In order to get your required resolutions installed, you'r going to need some trick. What I'd do is to use the old presets for the Polostar monitor in vmmaker.ini, these will create the variety of resolutions you're going to need:
monitor_specs0 15700-15800, 45-80, 4.000, 4.700, 5.300, 0.062, 0.062, 0.740, 0, 0, 288, 448
monitor_specs1 16100-16200, 45-80, 1.280, 4.500, 6.420, 0.062, 0.062, 0.740, 0, 0, 288, 448
monitor_specs2 25100-25200, 45-80, 0.200, 0.400, 8.000, 0.040, 0.040, 0.640, 0, 0, 384, 768
monitor_specs3 31500-31600, 45-80, 0.170, 0.350, 5.500, 0.040, 0.040, 0.640, 0, 0, 576, 800
In other words, you're going to need some method to have 320-line tall resolutions available in your system, so GM can pick them and apply the new settings on them.