I'm here. Just found this.
Perhaps the most useful mod is the grinding/polishing on the bolt handle, to allow it to slip easily back and forth in the bolt slot. That's what eliminates the dreaded "First Shot Flyer", which is caused by the bolt handle binding the firing pin. This was my favorite discovery/fix and almost anyone can do it.
Other fairly easy fixes are: 1. shimming and gluing-in the barrel, preferably with a new bull-barrel. 2. Glassbedding the action and installing a pressure pad in the forend (stiff stock forend required) with about 7 lbs of uplift. That anchors the rear of the action and makes the barrel-receiver very stable for each shot. (I've never tried the upward pressure trick with a factory plastic stock, but it works well with the target or deluxe wood stocks.)