I am curious to know how one distinguishes between "K" and "Late model" B230.

Mcbroom.com sheds a bit of light. Anyone else?

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The Early, K, and Late B230FT Motors and their Differences

Early B230FT: The early B230FT has garnered a somewhat undeserved reputation as being a fragile motor. True, of the four engine designs available in the 700-series cars, it is the weakest -- but it is still a rugged and reliable motor. There are a number of folks who have gotten 250+ reliable horsepower out of these power plants.
The important thing to know is where the weaknesses lie, and how to avoid having them come into play. The primary weaknesses of the early B230 are connecting rod design and crankshaft design.

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K Motor: The K motor is best thought of as an early B230 with a couple of improvements. Additional internal webbing was added to boost overall block stiffness. It got a redesigned axial bearing, but it is still located in the same position as that in the early B230. Unfortunately, it still has the same weak connecting rods as is found on the early B230. Thus, if one is contemplating substantial performance enhancements with their K motor, the same advise prescribed above follows here.

Late B230: Volvo went back to much of the earlier tried-and-true design of the B21/B23 when this motor was developed. Not only does it have much stouter connecting rods (13mm at their thinnest cross-section, compared to the earlier motors' 9mm -- a 50% increase), but the crankshaft was also improved substantially. The axial bearing was (re)located to bearing No.5 position -- the same place as is found on the B23. It also has the large, B23-style main bearing journals, which further reduce the possibility of flexing. It retains the narrower rod journals found in the early B230, however, but this has generally not been seen as a problem by the folks who have built up high-output B230FTs.