Thanks for the advice chaps. I can still get these OK, but they seem to be not listed in a lot of catalogues these days. Just a little concerned about long term availability, nice to have other options.
Another thing that slightly concerned me was that under certain rare and unpredictable conditions of lockup, this MCU will not respond to repeated reset pulses from an external watchdog. Usually needs power to be recycled. Not sure if this is a problem with this specific MCU or a general 8052 thing. Never noticed it with any other processor.