OK here is a reply from someone who has actually done what you are talking about.
I put my first set of 39.5 TSL's on an 8" Toy axle on Labor Day weekend 1987 (no that is not a typo). Total I have about 9 years of running this set-up. During this time my truck has always been my daily driver as well. I average ~35-40,000 miles per set before selling them. So you can see I get my use out of them. The trails I run are usually in Montrose or South Dakota although I have made the trek to CA two of the last four years in addition.
I don't have Long's either but I do have a home brewed set of Birfields I have been running for over a year. They are IMO as strong as Long's but are available for half the price. Anyway in the 9 years of running 39.5's I have never broke a Birfield. Before any of you think that I baby my truck think out where I said I run now and add the fact that the first 7 1/2 years were in the swamps of FL which is much harder on parts.
FWIW I am also the one who convinced Brian E. to finally run the 39.5's. Now he would never go back.
So what it comes down to is how much do you value the opinion of people who are guessing as to how it would work? That is up to you but I would say do it and never look back except at the guys with smaller tires who are getting their diffs caught on every pebble they can find.
