I know this topic has been hashed about a bizillion times, but...............
I have a Lock Rite in my '88's D35 and it's been in there for the last 16,000 miles. I also run 31" muds AND YES I DO WHEEL IT. I don't do rocks ('cause we don't got none) and I don't jump it or bounce the truck trying to get up obsticles. I am FAIRLY easy on the throttle. No problems.......yet.
Now, the other side of the coin..........I expect to probably break an axle sometime soon (I'm actually surprised I haven't yet) And when that happens, I plan on going with either the Superior or Yukon super 35 conversion with the Detroit and the 30 splined alloy shafts. I plan on running 31's for quite some time 'cause I have other mods planned that I feel I will benefit more from then going with monster size tires. Money is tight so this is the route that I have to follow. WHEN the time comes, I doubt I'll ever go larger then 33's, but that's not going to happen until I can do the change the right way not just slapping on a larger lift and bigger meats. I know a number of folks that are running some kind of 'super 35' kit with 33's and are pretty successful in keeping things together. Can they break them? Sure, nothings bulletproof. You can break ANYTHING if you hammer it hard enough.
Cheap is correct about the spool. That puts more stress on the diff then a lunchbox locker will and you will break before you even get to wheel that thing.
If you're bent on locking the rear, I would suggest you follow Woody's advice......"Go Lock-Right (and break shafts) or go home!"
PS. I would also suggest you swing by your local bone yard and pick up a set of stock replacement shafts, too. They're cheap enough and they'll get you home.
Steve