6.0 engine, mileage questions..

Heres the deal..I have a 1999 silverado extended cab short bed with the 4.8. This is our FAMILY vehicle. Well, turns out it has castech heads on it and with the mileage it has, its cheaper to just change the whole engine out. I decided i am going to use a 6.0 engine being they didnt have the castech issues the 4.8 and 5.3 had.. I HAVE to do something quick because we need this truck! using car-part.com, ive only found 2 locally and both of the yards they are at are not trustworthy! SO, I have found 2 more on the internet from trustable places, heres the dilemma..
1. 2002 silverado 2500 lq4 6.0...114k from lkq. Tested good but not run tested.
2. 2002 yukon XL with lq4 6.0, has 183k and i SAW a video of it running and ran absolutely perfect!

ok, i like the fact i saw the higher mileage one running, BUT, Its higher mileage..so, my question is, with the higher mileage 6.0 engines, was there anything that normally did not hold up much longer than 200k? I know if taken care of, the 4.8 and 5.3 engines usually went 300k sometimes with no issues UNLESS they had the castech leaking heads..Just trying to decide which one to get because i need this truck back on the road quick..I dont have the money to rebuild either of these, it needs to be swapped right in. Will do oil pan gasket and rear main seal also..
HELP!!

iv never seen or heard of a LS head leaking due to a casting defect...I personally believe that is a bunch of BS. I mean sure there might be a set of heads every once in a while that leaks due to a casting defect/flaw, but I dont think it is a very common problem. Find a cheap low mileage 5.3 and swap it in