"You have OD--but does it work. with the engine off, ignition on, flip the little lever and listen for a distinct click--that will tell you whether the solenoid is working--one of the most common failures."
Don't forget that the OD only works in 4th gear as well. When driving it in 4th gear at a decent speed (say 40+ mph) let up on the gas slightly and flip the lever. If everything is working it will slip into a '5th gear'. If it isn't, come back here for more detailed diagnostics.

Other parts sources:
www.gcp.se - great Swedish source of OE parts - exchange rate/domestic market/etc makes for really good prices - and shipping isn't really much more than domestic shipping
www.kgtrimning.com - best source for performance modification parts for pushrod Volvo engines I have ever seen.
www.swedishclassics.com - great domestic source for parts (though I've come to suspect they just resell www.gcp.se, et al parts with a hefty markup)
www.scandcar.nl - great source for rare parts for rare Volvos.

PS - Since you are new to 1800s - a couple of warnings learned the hard way.
1) NEVER EVER drive your car in the winter if they salt the roads where you live. 1800's have a complex body structure with lots of pockets and dead spaces which will accumulate salty road spray yet be immune to the most meticulous washings afterwards. And rusty 1800's are not economically restorable.
2) OIL those hood hinges - two of them on the front odge of the hood - by the radiator. They sit there out of sight and mind, yet exposed to road spray and grit from the grille. They are hard to oil properly, and when (not if) they get stiff and seize they will tear themselves off the hood (and you won't notice this as you lift the heavy back edge of the hood)