FJ55 fans and such
I read the article you pasted in and can share some thoughts. I've never seen an original FJ40 with a clutch fan- the latest year I've owned or parted was an 80, though. I have never seen an FJ55 with a fan clutch and have had quite a few 55's over the years.
My 78 FJ55 with stock engine has never overheated with the original solid drive plastic fan. Even letting the truck sit at idle in the hot summer it never overheats. The solid drive fan is more than adequate for the task of keeping the temps in hand.
Mark Whatley is right- there is not enough room in a stock FJ55 for a later model fan clutch. Even with the solid drive original fan blade there isn't a lot of clearance between the fan blade and radiator. Makes for great cooling but as I found out any unwanted movement in your engine mounts can put the fan blade into the radiator. Did that twice before replacing the front motor mounts. Cost me $400 each time to have the rad re-cored. Hope that never happens again.
I'm in the process of installing a later model (circa 87) 2F in my pig. I had hoped to be able to keep the later model water pump already on the engine but it looks like I am going to have to go with the original 78 water pump and pulleys. The earlier water pump is longer (taller if sitting on your workbench with the snout up) than the later model water pump, the fan mounting flange has threaded holes rather than studs, and the original 78 double pulley is really recessed backwards from the mounting flange. The original plastic fan blade attaches to the water pump flange with bolts.
I worried about having to use the original water pump because I didn't think it had the extra outlet for the hose that goes to the oil cooler. Wrong!!! The pump that was on the pig had a rubber cap over that outlet, secured with a hose clamp. I had changed all the hoses a few years ago and don't remember messing with that cap at all. It does look like all the hoses from the later model 2F will work right with the older water pump.
Clutch fans? I thought they were used to save energy, and to not run very fast until your engine temp started to come up.
To summarize, in my opinion with a 2F in its original location and a stock radiator in its original location there's not enough room in a 55 to run a fan clutch no matter what Toyota water pump you try. Gary S