Not off the top of my head. OP was over a decade ago, and believe Cisco now pulls much EoL documentation.
I can say, we commonly did such mixed feature stacks with the original 3750 series and later with mixed 3750/3750E stacks. (The latter to used 3750E 10g uplinks for the stack. There was a 3750G that came with a single 10g port but its supporting ASIC was only good for 8g.)
What you might still find documentation for, the stack election gave precedence to IP services over IP base, for mixed feature set stacks.
Lastly, Cisco over the run of those series, did change some of their licensing terms, so it's possible later IOS versions no longer supported mixed feature set stacks.
BTW, when we mixed feature sets, we insured two stack members had IP services because if only a single stack member did, and it failed, the remaining stack would lose all IP services features (until the IP services member was added back into the stack).
Although in the above, I didn't mention the 3750X, because my experience with those was in a different company and they didn't bother with mixed feature set stacks, but I believe it was still possible on those too. I recall the 3850/3650 series is when all had to have same feature set
Oh, and at least on the original 3750 series, all stack members didn't need to always run the same IOS version, but special rules for that.
