Significant Gen III Engineering Points

All Gen III truck engines use iron blocks. Only the Camaro (F-car) and Corvette (Y-car) LS1/LS6 engines feature aluminum blocks.

All Gen III engines have aluminum heads except for the 99 LQ4 engines that were equipped with iron heads. These engines received aluminum heads for the 2000 model year.

All Gen III engines share common main, rod, and cam-bearing journal diameters for ease of interchange. All blocks use a cross-bolted six-bolt main cap.

All Gen III engines are completely metric.

All valvetrain pieces are completely interchangeable. The standard rocker ratio for all Gen III engines is 1.7:1.

All Gen III truck engines use cast- aluminum oil pans that are deeper than either the Camaro or Corvette pans.

All intake manifolds interchange. The truck intakes are roughly 3-4 inches taller than the passenger-car intakes.

All Gen III engines employ reusable gaskets for all sealing surfaces except for the head gaskets. This makes it much quicker and easier to service the engine.

There are only two intake valve sizes for all the Gen III engines. Exhaust valves are all the same diameter.

Truck and Camaro engines use cable throttle linkage while the Corvette uses an electronic throttle. There are also some SUV engines with traction control that use an electronic throttle control.

Bellhousing patterns are the same for all Gen III engines. The crank flange is basically the same depth as the bellhousing flange.

The Gen III firing order has been revised from 1-8-4-3-6-5-7-2 to 1-8-7-2-6-5-4-3. Note that the pairings 1-8, 4-3, 6-5, and 7-2 remain the same, but the pairing order is different for reduced vibration.

The valve angle on all Gen III engines is 15 degrees versus 23 degrees for the original and Gen II small-blocks.

The Gen III bore spacing is the same as the original small-block, but each cylinder is ringed with only four head bolts instead of five.

taken from Chevy High Performance.