just backing up what everyone else has said..

4.3L good, auto good.

very strong motor in which it can take a decent amount of abuse and neglect and still run strong (not that you neglect your motor right?)

plus, if your truck comes with the LB3 heads, you can swap them out for L35s with no trouble. L35s go for about $200ish used. Get a P&P, new valves, and your set.