I was playing around with Crab Grab this morning and I think I came up with a MAME cheat that improves the control. It limits your movement to one space every time you hit a direction. You can't hold it down to advance multiple spaces. This helps eliminate accidentally moving two spaces. It also feels a bit more responsive. I'm still playing around with it and activating it isn't perfect but I like it so far. To activate it, start Game A and play for a bit. Once a crab advances upwards the code will kick in. It won't activate in Game B, but once it starts working in Game A, it will also function in B. Here is what I have so far:
Mega Man 3 by Tiger Electronics (and licensed from Capcom) has now been preserved in MAME
The game is based on the SM510. Sean has de-globbed and dumped the ROM and I've been helping out with digitizing the display and preparing the MAME driver. This is what the game looks like: