The engine would be a 5.7L (350). I have owned 4x4's for over 20 yrs and I have no idea what a 4x4 pin is but if its in the front axle is could be a costly fix. The ball joints are not a do-it-yourself job so that will cost some $$.
Unless you are prepared to spend some money to get this in running condition, you might want to pass on it. I am only guessing here but this could add-up $1000 more or less depending on what he means by 4x4 pin.
I drove a 1999 HD 3/4 ton 4x4 suburban in my job. I put 100,000 miles on it in 4 yrs and the only problems I had were brakes. We did use the truck as a GPS Survey work truck, carried a lot of gear, towed a lot, idled all the time (had over 5,000 hrs when tuned in in 02) and it went into some very remote areas and it never let me down. The brakes on the 3/4 tons do cost a lot more. Seems like when we needed brakes, its cost us $2,000 at the GM dealer. It was a leased vehicle and the maintenance was included in the lease so we had no control over who did the work as that was controlled in the lease. So I would look into the brakes real close as that could be another big expense.
And the gas mileage is going to be terrible, be thankful if you ever get 15mpg, as that would be the day to buy lottery tickets.