It is not hard to make 400-500HP from a stock 86-87 GN engine with only bolt on items. That is plenty of HP to move an S-10 quite smartly down the road. You don't need a cam, aftermarket headers or ported heads to reach this level of HP. Your engine can be reliable at this level if tuned properly.
Tuning is the key to making power with these little engines. If you can learn to tune the engine, and give it what it needs, you can make lots of power and not break stuff.
Bolt ons to consider: Larger turbo and larger downpipe, large cold air inlet system, larger injectors/better fuel pump, Chips and/or Engine management system. Alcohol injection, better intercooler.
These turbo engines respond very well when your remove the restrictions on the air inlet system and the exhaust.
Dave