I really don't have money, but I have available credit. I'm headed out of town tonight for a week, so I got some time to sort things out. Gonna wait a few weeks to get some cash built up then I can proceed pulling the block and doing it right. I have another engine that I was going to rebuild first, but this truck is more important. I have four vehicles now and only two run. One is for sale, it's a 2002 ZR2.
Credit is the devil. Literally the devil.
Not to be negative, but I wouldn't use it to get this particular truck running if you have alternate means of reliable transportation.
Given your description so far of the rest of the truck, it's going to be anything but reliable. Keep in mind I can't "see" the vehicle over the internet, but you are painting a picture of a very abused vehicle.
Translation: Money pit.
A toy (IE: mud truck) isn't something that should drain your bank account or run up a credit bill.
Just looking at what you though here was a simple head gasket change you are now into bottom end. You're slipping down that slope and it's gonna cost you.
I would suggest that if you intend to rebuild the engine, you pull it and strip it. Send it out to be hot tanked and do a quality bottom end. Then work on the heads.
Or cut your losses, abandon the current block and save your pennies for a decent drop in rebuild or crate engine.
Once it's back together, start in on the rest of the truck but just go to the solid axle you want. Rebuilding the IFS front end is money better spent on the solid axle if you intend to go there anyways.
If you've got an auto it will be a 4L80E in a 3500. 98 is kind of a crossover year for the 80 so it may or may not have the hardened internals and assorted "upgrades". It will be a rear oiler for sure, so that's a plus. Hollow input may or may not be there, the hollow is considered weaker. It may require attention soon also from the lack of maintenance this truck seems to have suffered. The 4L80E is a very robust transmission, but like all things mechanical it does not suffer abuse or neglect lightly. That's more money you might be spending. If the fluid is brown, it's probably old or at least has been overheated. Neither is a good sign.....