The Chevrolet 4.3L V6 is colloquially known as the "3/4 350" for good reason. This engine (which came stock in many top-line S-10s) is essentially identical to any 350 V8 engine of the same year--except that GM elected to lop two cylinders off the the block to make it a V6. This means that practically all tuning tricks and specs that apply to a 350 work on a 4.3L, and a lot of the parts are interchangeable between the two.
Induction
The first (and last) modification that many people make to their 4.3L is to scrap the engine's stock intake and exhaust hardware for freer-breathing units. First things first: if your engine has fuel injection, then toss your throttle body, computer and intake manifold into the trash and set it on fire. The only decent induction systems for this engine are made for carbureted induction, and aftermarket computer-operated fuel injection just isn't worth the money if you're not installing a turbo. Intake manifold selection for this engine is pretty poor, but the ones that are out there are pretty good. Edelbrock Performer RPM intakes are a popular choice, and Wilson makes one as well. Top your manifold off with a 2-inch carb spacer and a 550-600 CFM carburetor.
Exhaust
Like intake manifolds, exhaust header selection is a bit thin. Hooker makes a set of decent full-length headers for the 4.3L, but their headers have very small primaries and are going to limit top-end power. If you get the Edelbrock Performer intake, you'd be best off getting their matching exhaust headers, which are designed to work in the same RPM range.
Heads and Ignition
If you swap over to a carb, then you're going to have to swap in a new distributor to go with it. Fortunately, the standard GM HEI distributor used on V8s will swap over on most model years, and can be made to do so on all if you swap the cam out for an aftermarket one. As far as heads go, you're pretty much stuck with the stock ones unless you feel like spending several thousand dollars on a racing set. If you can acquire them, the earlier 1985 to 1992 heads flow a little bit better, but consider porting, new valves and larger 3/8-inch guide stud mandatory. Flow on even the best stock heads is pathetic; a good porting job and valve replacement are prerequisites for making anything over 250 horsepower.
Camshafts and Pistons
Fortunately, the 4.3L can use any piston designed for a 350 of the same vintage, so selection is through the roof. Just pick whichever set best suits your budget and compression requirements. Camshaft selection is equally simple. Any grind that will work on a 350 will work on a 4.3L, but you'll have to have a cam custom ground if you want anything above .500 lift. Off-the-shelf cam selection is pretty thin, and those available are fairly mild.
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