Never driven a C10 either, but the L-GATA is 1 of (if not) my favorite engines of all time. Welcome and good luck with your search.
A 20K budget should be able to buy you a rolling restoration, i.e a car that needs work but can be driven and enjoyed but isn't perfect and may need some minor rust repairs. If you get lucky you might be able to score 1 of the bargains that pops up from time to time, but you gotta be in there like swimwear .