I have two 3-speed wiper motor cores and am not sure what they fit. My '68-74 interchange book doesn't include them.

The first one had a "factory looking" sticker on it over the stampings that said "3431077" and "73692", but when I peeled it off the stampings are "2926919" and "73692", w/ "1091 G" under those.

The second one has the stampings "2983033", "73691" and "3028".

Your first one is what I call a sticker motor.
It came from the factory or over the counter parts when they would run out of correctly stamped 077 motors.
Yellow stickers for 3431077 and blue for 2983116 motors.
The 2926919 number underneath is for a C body 69-71.
Your 033 motor is for a B body late68 date code and would go on an early 69 car.
1091 is the 109th day of 1971 or April 19th , 1971
The 3028 is the 302nd day of 1968 or Oct 29th, 68

NOS over the counter motor.

Yep, that's EXACTLY what the sticker looked like... right up until about 15 minutes ago when I peeled it off.

Thanks for the detailed breakdown, too.

FYI, this post is also related to another one I have on the Q&A forum about wiper interchangeability: https://board.moparts.org/ubbthreads/show...e=0#Post7064086