Truck Forums - 4.3 head swap

Here is some Wiki history on your 4.3L engine that might change your mind on your possible mod, depending on which 4.3 you have.

V6

4300

Main article: Chevrolet 90-Degree V6 engine
The Vortec 4300 is a 90° V6 truck engine, replacing the Chevrolet 250 in light trucks and 200 cu in (3.3 L) and 229 cu in (3.75 L) 90-degree V6s in passenger cars. The 4300 is based on the 350 cu in (5.7 L) Chevrolet small-block V8, and first appeared in 1985 with the throttle-body injected LB4 in passenger cars; light trucks and vans used Quadrajet carburetors for 1985. In 1991, the limited-edition GMC Syclone featured a 280 hp (210 kW) and 350 lb·ft (475 N·m) turbocharged and intercooled LB4 with the first use of multi-point fuel injection on a Vortec V6. The central-port injected L35 (Vin 'W') debuted in 1992; the cylinder block was slightly changed, a balance shaft was added to remove minor vibrations, and better breathing yielded 200 hp (149 kW) . Another CPI engine, the LF6, joined in 1996 with the introduction of Vortec cylinder heads, while the LB4 was retired after 1998. In 2002, GM introduced a new multi-point injected LU3 engine, and a LG3 variant appeared soon after. This engine's origins date back to 1955, when the original Chevy small-block V-8 was introduced.
All Vortec 4300s use a cast iron block and heads with a 4 in (101.60 mm) bore and 3.48 in (88.39 mm) stroke, both of which are the same as a 350, which gives them a displacement of 262.39 cubic inches (4,299.8 cc). Connecting rods still measure 5.7 in (144.78 mm) although the rod journal diameter is 2.25 in (57.15 mm). 1992 and later cylinder blocks used a different timing cover since these engines used a balance shaft (some 1992 production cylinder blocks for the LB4 with TBI induction used the 'traditional' front timing chain cover from the small block Chevrolet). This change created a situation where most aftermarket timing chain alternatives do not fit. This is true of gear drives and double roller chains. They are pushrod (center camshaft) engines with two valves per cylinder and are produced in Tonawanda, New York and Romulus, Michigan. Power output of the new LU3/LG3 engines is 200 hp (149 kW) to 215 hp (160 kW) and 250 lb·ft (339 N·m) to 265 lb·ft (359 N·m).
4300 applications:

1985–2005 Chevrolet Astro/GMC Safari
1991–1993 GMC Syclone/GMC Typhoon (See LB4 below)
1988–1995 Chevrolet Blazer/GMC Jimmy
2001–2002 Chevrolet Express/GMC Savana
1988–2003 Chevrolet Silverado/Chevrolet S-10/GMC S-15
1994–2001 Oldsmobile Bravada
1985–2001 Chevrolet C/K
Toyota Forklifts 7000 lb Capacity and up

LU3 applications:

Chevrolet Astro/GMC Safari (base models)
Chevrolet S10 Blazer / GMC S15 Jimmy
Chevrolet Express/GMC Savana (base models)
Chevrolet S-10/GMC Sonoma
Chevrolet Silverado/GMC Sierra (base models)
GMC Envoy
Isuzu Hombre (optional)
Oldsmobile Bravada (base model)

LB4 applications:

1991 GMC Syclone
1992–1993 GMC Typhoon