It’s low kms 137,000 looking at the long run get way better fuel mileage with a tuned 4.8 LS Plus make some huge horsepower on 87 fuel Thanks for the compliment on the truck I think I found the unicorn still has the original window sticker from 98 lmao and all documentation.
Oh, dang! I just realized the metric mileage, LOL. That's low!
In that case, I personally would just leave it alone. Nothing wrong with running the engine you have. I can understand a high mileage, worn out SBC getting swapped for an LS mostly just due to cost (junkyard LS is cheaper than machine shop-ed SBC,) and other reasons, but not a low-mileage runner. Go find yourself a beat up RCSB and drop your LS on that! Or better yet, just get a NBS with one already installed.
These trucks don't get spectacular gas mileage, LS or SBC. They are after all pretty darn heavy. Unless you go turbo over NA, I don't see a reason. I'm sure you have a plan, so don't let me steer you otherwise, LOL. Just my opinion.
I hope I helped answer your initial questions. And since you mentioned it, more reason to go with the 80e series if you go boost.