Yup! I have some on hand, but the DUART only takes a single clock line and I didn't have the parts for to build the crystal driver. This particular 8051 has a built in one, but no oscillator out. Was contemplating using one of its timers.

I didn't even realize the AVR supported a clock out until I bumped into it in the data sheet. Maddeningly it's not broken out on the Arduno Mega =P.