it's really a "stock" application circuit, similar in most respects (aside from the external oscillator

This is not "knowledge" but "recall" which may be faulty :)

Do you not have to apply extenal oscillator to XTAL2 for the steam driven derivatives?

from "the bible"
Note that in the NMOS devices (8051, etc.) the signal at the XTAL2 pin actually drives the internal clock generator. In the CMOS devices (80C51, etc.), the signal at the XTAL1 pin drives the internal clock generator. The internal clock generator defines the sequence of states that make up the 80C51 machine cycle.

Erik