Ouch!!
I am sorry to state. Unfortunately, 65816 CPU will NOT WORK on Apple
II+ nor Apple //e because 65816 CPU's and 6502 CPU's timing are not EXACT
the same. They have different nanosecond measurement. For example, 6502
CPU requires 400 ns to run while 65816 CPU runs 250 ns (I can't remember
exactly.)
"Understanding an Apple //e" manual stated that someone tried to plug
65C02 CPU into Apple II+, but very several instructions work while often it
crashes at all times.
It would be ideal to redesign motherboard that it will have Apple I's
Apple II's, Apple II+'s, unenhanced Apple //e's, enhanced Apple //e's, and
Apple //c's ROMs to be BUILT in one motherboard using 65816 CPU. Do not
worry that nanosecond measurement may not be the same, but the measurement
of MHz will match. All Apple Models can share single 16MB RAM.
You can be able to run all Apple Models continuously in the same memory
without needing to switch back and forth. I like Vince Briel's idea to
replica Apple I, but I suggest him to do the same what my suggestion states.
My project allows to have 6502, 65C02, and 65816 CPUs to be built in
software simulation. My software simulation does support 6502's Bug with
invalid ADC & SBC's N, Z, and C flags however it is undocumented until I
notify when it is ready. It would be great for the experts to be very
curious to experience with 6502's Bug.