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I’ve made some progress. Thanks to the dot clock info on this table:

I was able to get Battle Garegga dialed in:

Line5x mode 512×240 optim.
Sampling phase 202 deg
H. samplerate 432
H. backporch 46
H. synclength 41
H. active 450
V. backporch 18

It’s a little low of center on the screen but I can’t get it to shift any higher. Maybe that’s how it appeared in arcades?

Also I was finally able to nail down Espgaluda:

Line5x mode 512×240 optim.
Sampling phase 292 deg
H. samplerate 640
H. synclength 80
H. backporch 46
H. active 450
V. backporch 13

It turns out it’s a PGM board even though it’s not a cartridge so I used this line:

68HC000FN20 – Motorola 68000 processor, clocked at 20.000MHz (PLCC68)

from here:

to test dividing 20MHz by a few different integers that made sense until I came up with:

( ( 20000000 ) / 2 ) / ( 263 × 59.34 ) = 640.76194

To figure out the sampling phase I’ve been testing for an upper and lower boundary where the pixels will start to flicker or appear out of place, and then I average those two numbers. It actually seems to work really well.

I’ve been using the table here:

Fine-tuning of sampling rate in optimized modes

and the Horizontal multiplication factors here:

to try and optimize H. s.rate adj but so far anything but zero looks worse even if it’s closer to the calculated exact samplerate.