The B23FT into a 140 is possible.I put a B21ft into my 145 last summer and then a B230FT in November.Your on the right track going with a B23.There were several issues changing to the B230 that made it more complex than anticipated.
You will NOT need to make custom manifolds.I used stock volvo intake and exhaust.I also used all stock volvo intake plumbing except my air filter,airfilter mount and a 3" peice of plastic pipe from the hardware store.All the cooling system hoses are stock volvo with the exception one of the heater hoses,(a piece of bulk 3/4" heater hose).You'll need to deal with: Master cylander mount,motor mounts,alternator and of course fuel system plumbing and wiring.
Some people seem to be down on the swap and will try to scare you with speculation about what you'll need to fabricate or change.Having done 4 V8 swaps on volvos as well as other chevy swaps (jeeps and stuff) I can tell you it was easier than those and it gets more looks at the shows.The V8's seem to handle like dump trucks even when set up right (especially the big blocks).
You could gain more horse power supercharging the B20 but my experience has been that when they that souped up they get tempermental,also try finding parts just anywhere!You'll get better gas mileage,cleaner emissions and better reliability with the B23ft.You'll love how you suprise people in your smooth running quiet volvo when you blow their doors off! It will be quieter cruising down the road at 130 (done that).Parts will be more available.You won't get tempermental running with severe altitude changes.I can think of more benefits given time.I have had several souped volvos and like my B230 145 the most.
Cameron claims 155 rear wheel horse power with his supercharger.the 740 with a B230ft claims 160 stock (probably crankshaft horsepower though).As I've told several people the most impressive aspect of the car is the pick up you'll have when cruising.It's awesome! You can coast down to 50-55 in overdrive and step on it and it picks and goes,right now!
I drove my car 1800 miles last weekend to the IPD garage sale and never popped the hood except to show the car.I also drove from Redding to the Oregon border without coming out of overdrive! It steers well and stops great.I say go for it! I will try to host some pictures on line.