There is tons of documentation on the center seam moc for eastern woodlands cultures.
A couple of tips..., Carl Dyer makes a good leather shoe..., most places/event out East they aren't considered mocs so are considered modern footware (don't flame me folks I don't write the rules)...., but if I had a guy who had a choice between Dyers and modern orthopedics (and I do have such a guy) then the Dyers are a better choice.
Otherwise the Townsend kit is a good starting place...
Mocs stretch went wet, and they need to be snug. So when they get damp, (or you can get them wet and wear them) they will stretch, and you should adjust them at the heel to make them fit again. Once this has been done one time, then grease them for water resistance if you wish.
NOW when they wear out..., if they are a good fitting pair, don't throw them out..., cut out the stitching and use them as a pattern for the next pairs. Most folks that wear mocs on a regular basis have two to three pairs with them at a weekend event or trek. Put on the next pair when you get a hole, and repair the damaged pair, or replace when wet at night to keep feet warmer, etc.
LD