Well, an engine swap is only really worth it if get more power out of it, right? A standard b23 without at least cams and a little bit of work feels sluggish even in a little toyota starlet....
If you can find one, a b234 (16v) could be a nice option. Head looks really nice to. (although mine looks a bit dusty

) Well made, big ports, etc. Should easily get you 170 bhp with a bit of attention to detail. The only downside to the b234 is that tuning parts aren't easily available for that head in the uk. So if you want more after a while. you might have to look for parts from scandinavia or the u.s.
On the other side, a b230ft (8v turbo) should slot in there nicely with the exception of the turbo & manifold. That's easily solved though. Go on ebay or turbobricks, and sort yourself an aftermarket turbo manifold. Maybe this one? put it on upside down, or try to source a genuine topmount manifold.
http://cgi.ebay.com/ebaymotors/VOLVO-24 ... 2258wt_941
If you can, try to find an engine donor with a gold ecu, rather than a black one, as you gan get chiptuning for the gold ignition box. All fuel ecu's can be chiptuned. No matter which engine you choose, LH-2.4 from a 240 is a plug&play loom for any b23 version & ecu. It's what's normally used for conversions on 240, 740, & 940's.. As long as you know which wires to join to the car, the rest should be fairly straight forward.
Anyway, after doing a conversion, your problem should be putting the power down, rather than be slow.

Good luck!
PS. These are the different ecu's you'll be looking for:
Gold ign-box. remappable. 94ft Black ign-box. No remap. '93ft
My current stock. (not for sale... )
93ft ign , 94 ft fuel, 94 ft ign
91 16v ign 91 16v fuel.
