IIRC, the 4 lever one is for 60-63 and the 3 lever one is for 64-66 and the one knob thriftmaster is for 60-66. Personally, I have never seen a 2 lever heater in a 60-66 truck.
I've got a 2-lever heater in my '62. I've seen lots of them.
I thought this was the "standard" heater.
The heater core, box and motor is mounted to the firewall inside the truck, under the glovebox.
One lever runs the motor: Off/Low/High
The other lever moves a cable that changes the trap door in the heater duct to defrost vents or out the end to blow heat out under the dash...and let it just sort of go where it wants to.
With this heater, there is ALWAYS hot water running through the heater core, and you can't run the defroster without running air over the heater core. It makes getting the fog off the windows in the summer a hot ordeal.
The Deluxe heater has the box, core and fan mounted under the hood. It has four levers, but I don't know what they do just yet (I have a complete system I'm going to restore for my truck). I believe with this style, you can run air thru the defroster vents or under-dash vents, without running it over the heater core.
I've never seen a 3-lever panel or system, but that doesn't mean much.
On the '60-'63 systems, the panel with the levers has four vertical slots in it, with a piece of black rubber riveted to the back side of the panel. The ones I've seen have a slit in the rubber for the levers. On my two-lever panels, the slits were not cut for the outside levers.
-Brad