Or you could just add a CPU frequency switch to the driver itself, similar to Novag Super Expert.

I did look around for the "Mega-4", but can't find any evidence that it was ever released.
More information about this machine: http://spacious-mind.com/html/great_...ine_4_mhz.html
"So the question needs to be asked was the Destiny MEGA-4 GGM ever released? Where there any made at all? Most sources say no."

The 20MHz version by SteveUK(?) probably has ROM modifications for the changed timing.