Some time ago, I posted a question asking about the Motorola SC44125P CPU, and I eventually determined that it is a custom 6800 with pre-programmed, dedicated data bus (8 bit) and address bus (16 bit) pins, along with the 6801 instruction set. Although it has the option, neither the on-board RAM or ROM are used.
After some brief comparison of later 68xx CPUs, I see the 68HC11 comes closest, but want to know which would be a suitable version (or newer replacement) that would work the best.
6801 or 68HC11 instruction set
Ability to disable on-board RAM / ROM
Dedicated 16-bit address bus pins or the ability to easily program same
Dedicated 8-bit data bus pins or ability to program same
Support pins required: R/~W, Clock input (1MHz), ~IRQ, ~IRQ2, ~NMI, and ~Reset
If you're attached to HC11 assembly code, maybe you could use a 9S12 to upgrade your design. At those ancient times it was said it was assembly source compatible, although object code was not compatible at all. You could check AN2708 which deals with External Bus Interface on the HCS12X.
Sorry all the HC11 is obsoleted
So I can not recommend you any HC11 device.
If you want you can move to the S08 family like the mc9s08pb family
I hope this will help you