The first generation B230s had smaller crankshaft main journals, along with 9mm connecting rods. The 9mm connecting rods gave trouble in the turbo cars, especially.

In 1988, as a running change, Volvo increased the size of the crankshaft main journals, and moved the thrust bearing from the center main to the rear main. These are K block motors.

In 1989, Volvo changed the thickness of the connecting rods to 13mm, from 9mm. These are still K blocks.

About 1990, Volvo changed the oil galley configuration to more easily accept piston oil cooling jets. These are still K blocks. No piston oil cooling yet.

In late 1990 Volvo changed the soft (freeze) plugs from the dome style to the cup style. I like the cup style better. Still K blocks.

In 1993 Volvo added piston oil cooling. These are L blocks, and also have the curved tooth timing belt. The cylinder walls are thicker, too. These are rugged, but not sophisticated, engines. The piston oil cooling eliminated piston slap and lubricated the cylinder walls quite well. These engines last even longer with regular oil changes.

The piston length never changed as near as I can tell.
--
john