Cant recommend too much in the way of reman engines... honestly, if it were me, given the value of KJ's nowadays, and knowing what a reman is going to cost you to get installed, I'd be more inclined to use a low (relatively) mileage salvage engine from a wrecked, known running donor vehicle.
250,000 miles on the truck itself, if maintained and repaired, isn't too much of an issue (although I would wonder about the transmission next), but putting 1500-2500 for a reman engine in, well, it seems disproportionate to me.
Might want to just do some price and availability checking on a salvaged engine in your area. I mean, crap, if you can pick up another 3.7 with anything under 100k miles for anything in the area of $500-$700, less than a grand and you can be back on the road with an engine that will go another 100K or more miles, and still have cash in the pocket.
It's going to be the same, if not slightly less work to use a salvaged engine as it would a reman.
Good luck.