Ok, Here's what's involved with the conversion and what it will get ya.
1. The B-21 and 23 are designed to be tilted. This is for oil draining in the head and oil pickup in the pan. You can angle the motor up straight but that's not the way God and Volvo ment it to be. That said, there a few things you have to do to mount the engine. If your not going turbo (I don't know of the turbo fitment issues) the stock exaust manifold hits the right side frame rail so the frame rail must be trimed slightly and rewelded. There also clearence issues with the altinator and the ideler arm of the stering. Now that you have mounted the engine and figured out the altinater problem there is the transmition to deal with. My friend that is doing this swap in his 70 142, used the 4sp+od that he got with the B-23 and of course that ment cutting and welding in the later transmition tunnel into his car. Now that that's all done, almost any intake system you can think of will not clear the brake booster, hood and master cylinder. My friend is now trying to track down Webber side draught manifolds in order to use TWM throttle bodies and electrimotive FI. So you can imagine the cost of this ordeal.
2. Once you put in a B-23 or 21, there is not that much performance stuff for them. I have heard if you get a cam, port and polish the head, boost the compression and add Webbers or some sort of trick EFI (Electrimotive) these motors can have good usable power around 175bhp and lots of torque. I have a modified B-20 in my 145 and it will be interesting to see the performance difference in the two cars when his is on the road.

john