There are two types of B230---the crankshaft was enlarged (back to the original B23 size, more or less) on the later ones. They will outlast just about any Honda. A car I used to own (89 740) now has 350K miles (not KM) and the engine is all original---never been apart, never even had the valves adjusted. I'm sure it could benefit from a freshening, but it runs OK and doesn't use excessive oil.

All engines have a thrust bearing of some kind. On newer designs it is often integrated with one of the main bearing shells. The use of a separate thrust washer is perhaps slightly archaic from a design point of view, but is not in any way a durability issue, as long as the size of it is adequate for the load involved.

I would define torque as the ability to lug at low revs (which my B230 does just fine at, from 1500 RPM up, pulling a 3.31 rear) and flexibility as a broad torque curve, with consistent power available over a wide range of engine speed---not peaky like a race car.

A heavy flywheel, as found on a stock Volvo, has a lot of inertia. This makes the engine less eager to rev, as the additional mass must be accelerated. It makes no difference at a constant speed, when it serves to smooth out the firing impulses.

It seems to me that the design of the B230 in no way inhibits its revving ability. It has all the right design elements---way oversquare and cross flow head. The poor breathing is primarily a function of the intake manifold design---the exhaust is about as close to a header as you can get without actually having one. (smooth curves, 4 into 2 into 1 layout) In general, long intake runners increase torque and short ones let the engine rev. A properly set up (stock) B18/B20 with SUs will rev out well past 6000 RPM in spite of its less efficient valve layout and heavy flywheel.

The cam has a lot to do with it, probably more than any other single factor. The stock unit is a compromise, attempting to satisfy many different requirements---power, smooth running, torque, engine life, fuel economy, and especially, the legal requirements of emissions standards. This last factor tends to rule out cams with a lot of overlap, which is commonly increased to boost performance.