You probably need to make GM trigger the PAL preset of your PVM. We don't know which specific param the PVM uses for this. It could be the frequency, or the total lines, or both. So you need some testing:
First try these 2 separate configurations to see if any of them works. In mame.ini, change this:
monitor custom
crt_range0 15750.00-15750.00,49.50-65.00,2.000,4.700,8.000,0.064,0.192,1.024,0,0,192,288,448,576
Then, try this second option:
monitor custom
crt_range0 15810.00-15820.00,49.50-65.00,2.000,4.700,8.000,0.064,0.192,1.024,0,0,192,288,448,576