The most common causes of uneven exhaust are indeed worn out or misadjusted valve gear, regardless of the type of valve gear - but the comment was the "wheels can't get out of square" and they can! Being grossly out of time due to bad valve gear is only slightly less egregious than a bad axle or wheel center and the thing should be put down and fixed in either case.
I too fired and ran a locomotive for years with Southern valve gear - it's simplicity is hard to beat. If yours didn't sound like this, it was probably worn out and needed to be rebuilt. https://www.youtube.com/watch?v=kLFEKPc ... BIHoynkNfe

Here's some my videos on MISS 76:

Mississippian 76 (Restoration Tour), 06-26-2013
https://www.youtube.com/watch?v=Cb9DJX17_yk

Train Expo 2014 (Mighty Mouse & Mississippian 76), 06-20-2014
https://www.youtube.com/watch?v=Phbk1UFSPnI

Mississippian 76 (Restoration Tour), 06-20-2014
https://www.youtube.com/watch?v=v0tl00GOeZc

Other MISS 76 Media

Gettysburg/Mississippian 2-8-0 76 Update by RailsOfMichigan
https://www.youtube.com/watch?v=nlOnNmOu2io

SLSF 76, RRPictures Archives.net
http://www.rrpicturearchives.net/LocoPi ... ?id=124640

Mississippian 76, Owosso, MI 7/23/15
http://metalheadrailfan.deviantart.com/ ... -548564147

Facebook, SRI Videos MISS 76 Project
https://www.facebook.com/steamrailroadi ... 267444479/

Facebook, Explorers Post 1225 Caretakers of MISS 76
https://www.facebook.com/explorerpost1225/

Enjoy! ^_^

Drivers are pressed on the axles, but they are also keyed to the axle to keep them from slipping. BIG keys.

Not all drivers are keyed. Not all keyed drivers are known to be keyed. Some guys that should have known better created an interesting situation for me some years ago...... huge amounts of unnecessary drama which prevented real work for months of dithering.

Guys - valve setting is not refining the engineering on the space shuttle and once you have worked through it a couple times with experienced people isn't that hard to understand. It was done every day with hand tools and big hammers 150 years ago in the flickering light of oil torches. I think the situation at hand was probably that of an operation running on the ragged edge of marginality without sufficient down time to do more than minimal maintenance - which certainly caught up with them in serious ways a little later on.

Nobody has said anything about the staybolts yet?

This is exciting news. I rode behind the 76 at Gettysburg a week before the infamous boiler event with the CP 4-6-2. Probably one of the last times she operated.