Have you heard about the LCDmod? I found this video and if you could code a patch it might be worth having that option available for physical carts ;) I’d buy it lol
It looks like these hacks are simply compensating for the input lag by delaying the on-screen flash. I’ll try the duck hunt hack to verify, but I believe the player sets the delay time manually in the menu.
A lag calibration tool would be nifty, but just setting the delay in milliseconds via a menu option would be enough to get Gunhawk working on LCDs afaik