What is this MAC driver for? I remember modifying a flat blade to a similar shape to remove Triumph and BSA clutches in the old days.Total length is 5 1/2 " and tip is 1/2".

Hello, Papaw. Do you think it is this one??

The cut of the blade on that one is different. Mine is a definite V shape.

Could the one you have been modified?

Doesn't appear to have been modified.

The tappet driver is flat blade with an ear on each side to keep it from sliding off the adjuster when using. I have seen the V cut ones before but not sure of their use.

I looked all through my 1966-67 catalog and did not see the v cut driver.  You could buy just the handles separately.  Perhaps someone bought one and put that blade in it.

I never saw one , but I'll guess that you can use it to install or release a spring with a shepherd hook, like a brake spring. Also could use it to release stuck rubber hoses?

Don't know the original use , but kind of like using a screw driver for a prybar or chisel .

This has gotten me into some deep diving and I have come up with no real answer, but I did find this-
The spanner[63] or Snake-Eyes (trademarked)[64] screw drive uses two round holes   (sometimes two slots - the same driver bits work in both types) opposite each other and is designed to prevent tampering. Other informal names include pig nose, drilled head or twin hole.[65] This type is often seen in elevators and restrooms in the United States, the London Underground in the United Kingdom, some train wagons and the Montreal Metro in Montreal, Quebec, and is seen in all Panama Metro wagons. The driving tool is called a "spanner driver" or "spanner screwdriver"[66] in the US, and a "pin spanner" in the UK.[citation needed] They are also often used for soft spikes on golf shoes. The US military's M17 and M18 service pistols (variants of the SIG Sauer P320) use spanner screws to dissuade disassembly of the handgun beyond normal field maintenance except by the authorized armorer, and they had also been used previously for reinforcement screws on the M14 in order to secure the front locking tab on the magazine well.

The knife and gun manufacturer Microtech uses a variation of this with 3 round holes arranged in a triangle shape. The camera company Leica Camera has used versions of this on rewind knobs and other levers on their rangefinder cameras.
   

From a Wlikpedia link. https://en.wikipedia.org/wiki/List_of_screw_drives#Spanner