I've now got everything working at 4MHz with either the NMOS or CMOS part. This after much messing around!
I've now got a "proper" clock module giving 8MHz as the main clock and drive all the other chips from the XTAL/2 line (to get proper 50/50 duty cycle). Also the clock is now buffered seperately before going to the bus.
I still am getting the odd glitches though that disturb interrupt operation but I'm not sure why!
Anyway I've now added a CTC chip and am exercising this with some code. More schematics and code to follow soon....