Anybody know if you can install a 5 blade fan on my 1962 PV to replace the factory 4 blade, in order to increase the cooling a bit?
If so, where do you find them, and what modifications are necessary (i.e. different front pulley, etc.?)

Going to a 5 bladed fan may be more complicated than you think.

5 blades push more air than 4 if the length, width and pitch of the blades are all the same.

The incorrect 5 bladed fan may be worse than 4.

Why do you want more cooling?

I first thought that our '64 544 was getting hot under certain circumstances - hills, stop lights, etc.

After a 3 hour parade where the gauge went up and down, I found that the cat never really got hot - and I have a B20 engine. My gauge is sensitive.

Modern cars often have circuitry to keep the gauge steady - in some later Volvos , if your gauge shows hot, the car is REALLY hot.

A new fan may just be a band-aid. Find out how hot your car is really getting and find out why it is too hot.

One easy thing is to borrow an infra red gauge and look over your radiator. Your local FD might try this for you if they have an instrument

some cylinder heads have cooling tubes in them that can rot out and disrupt cooling.

If your car is really running hot, a better question might be - "Why is my B__ engine getting too hot" You might get several suggestions from brick boarders who have solved this problem.

Personally, in 50 years of driving, I have never had a problem, but in reading auto magazines all that time, I almost never seen a fan solve the problem, unless it was clutch fan that went bad.

The one thing that I have seen several times is some one removing the cap off a hot engine and blowing scalding water 20 feet on the air.

Once we had a Dodge van come into our fire house that could not be turned off, pulling the plug wires did not stop the engine - using a carbon Dioxide fire extinguisher in the air cleaner did stop it!

The late Volvo 5 blade asymmetric fan is supposed to be a bit more efficient and run a little quieter. They are plastic rather than metal. Not sure if they were fitted as stock to any model? Not cheap and I would say that they aren't a cure all for cooling problems. A rad that needs at least a good flush or a recore a more likely cause or a poor water pump. Pattern pumps with pressed steel blades can be poor. A genuine Volvo bypass type thermostat also recommended.

my 122 had problems cooling. I took the rad apart, cut some wooden sticks to just fit the rad tubes and pushed all the stuff stuck in there out..
I removed both the top and bottom, If I did it again I'd try to just remove either the top or the bottom.

after back together I put it in a sink and pressure tested . i had a couple of spots to chase with a torch and re solder but not too much..
If you want to spend, a rad shop can do it for you..

in my cae that made a huge difference , I went through similar issues in my ford van and in that case just opted for an aluminum rad.. it works fine but if you care about originality I'd keep the orig fan and copper or brass rad
the rad shop I went to with my ford rad had a tank of molten solder, makes getting it apart easier. I used a plumbers torch and just circled the seam until it came apart. I tinned the mating parts to make sue they would solder ok before I put it back together. I think selling a new ford rad meant lass labor for him..but he was capable. it was on first in Burnaby, a couple blocks west of boundary road..

I needed a water bottle so I soldered up a 2" tube of copper with a cap ont he bottom and think I used a 2":1" copper pipe reducer, then fitted the parts , probably from an old rad so I could put a new rad cap on...
the OEM rad has a a cap but it doesn't have a pressure relief valve. if you remove it and look down you can see some of the ends of the tubes. My take is those are plugged up. I used good old lead solder not the new style lead free solder.

i removed top and bottom but if I did it again I'd pick and just remove one or the other. I cut wood sticks on my tablesaw to fit fairly loosely and went gentle at it , you can always cut a bit larger sticks later.. If you are inclined to DYI It can be done, you can take your own appropriate cautionary measures about the lead solder being poisonous.