You will be disappointed in flat screen lcds I tried to do this with 2 off-road thunders and ended up getting my originals repaired by skip from coin op service for less than 100 bucks. The problem is that the colors are made to look good on crt and play to the scan lines. I tried just about everything before giving up...converter boards, scan line generators, monitors vs TV...just get the originals repaired by skip...totally worth it.

Btw the vertical hold sounds like a relatively simple fix...I assumed you tried adjusting it via the control board?

Hrmm ive seen orts and mario kart gp 2 conversions.. Both looked better with good crt monitors. Brighter colors, no notable pixelation...I've seen these side by side too.