Atari Anguna: bugs on a sixer

First, a brief bit of Atari history:  The original Atari 2600s had 6 switches on the front -- the power, B/W, Select, Reset, and one difficulty switch per player.  Later models moved the difficulty switches to the back.  All the Atari versions now have goofy names that the collectors call them.  The original "heavy sixers" were bigger and heavier than the "light sixers" but both are sixers (having the 6 switches).  You could also have a 4-switch "woody" (that still sported the awesome late 70's wood-grain), or the darker "vader".  Or poor saps like me have the cheap little re-released Junior.

Well, I had only tested Anguna on my Junior, and a 4-switch woody (and in the Stella emulator).  It worked fine, so I figured we were good (theoretically, all the models are supposed to work the same).

Well, I just found out that that's not the case.  The main character doesn't animate correctly on the sixers.  I'm not completely sure what to do about it -- how do I debug a problem that only shows up on hardware I don't have?

Current possibilities, from least to most painful:

1. Somebody on the AtariAge forums has a guess about a possible difference in the hardware, and I can just go fix it (this would be a long shot)
2. Get a sixer.  That means either buying one (maybe $50 if I'm lucky) or borrowing one.
3. Make changes. Email them to someone with a sixer. Wait for report. Try again.

Ugh.