Very interesting. Volvo upgraded the connecting rod size in the B230FT as a running change in the 1989 model year. I suspect you had the early, small connecting rods. Yes, the B21FT will work fine, although the lesser displacement and lower compression will lower your performance. You will need to drill and tap the block to accept the knock sensor. The turbo drain pipe is in a different location on the B21FT, and that detail will need to be worked out. You will use the water pump fromm the B21FT. Make a plate and a gasket to cover the B21FT distributor hole. Where are you? I have a B230FT short block that is surplus.