That price is a steal. The veggie oil kit alone costs $2k.
The 1991's came with the older 6.2L IDI NA diesel. I know because I have that exact truck in the same color. Badge says GMC though. You can add a Banks Turbo (I did) but it's neither cheap nor a breeze. However, if you are in a truck happy place like Texas you stand a better chance at finding a used Banks unit on the cheap. Also, I'd recommend using a waste-gated turbo from the Banks kit for the Powerstroke 7.3 IDI. Mates up well and gives better power down low, which has been my only complaint on my turbo.
Fun story: my alternator died mid trip in the woods in the snow last week. Then the batteries slowly ran out. But because there is NOT ONE ELECTRICAL PART in this engine, I was still able to drive out to the nearest town for help because the engine won't die unless you tell it to. Try that with a modern diesel or practically anything else on the road.