See the archives. For the 240 and 740 it's a piece of cake. Well, maybe. It actually depends on your skills as a baker.

For the 850-SVC70 it's probably much saner and cheaper to sell the car and buy a 5-speed. Besides the transmission and clutch, there's the pedal cluster, console, linkages, the ECU, the wiring harnesses, probably about a bazilion electronic sensors, and probably about a dozen other items that I haven't thought of. It would be best to locate a wrecked donor car, park it alongside and sequentially transfer all the differing bits and pieces.

Also, the 5-speeds are worth less on the "pre-owned" market and since 97% of Volvo buyers don't know or want to know a clutch from a soccer ball they tend to hang around the dealer's used car lots for ages. You might be able to engineer a trade with a dealer. Try e-bay, also, they show up there when the dealers get tired of looking at them.

Good luck!