There is also an "A" tank which is Auto I believe. "B" tanks are a little longer but will work. "MC" is for Motorcycle and is a smaller diameter.
I looked up the sizes in an old accessory catalog back in August:
Prestolite Model A = 22" x 7.25"
Prestolite Model B = 20" x 6"
Prestolite Model E = 16" x 6"
Standing: A on left B on right. Although it may be the one on the left is an E according to the above dimensions.
Just based on what I have been told.
OK. I stand corrected. Above left is the shorter tank and has an E on it. Right is a taller tank and has a B in the serial number. Make sure if you use one on a running board that the valve is offset and towards the top.
The tanks come in two styles. Center valve and off-set valve. The center valves are used upright and the off-set valves are set for horizontal mounting on the running board as on our early 13 Touring shown below.
And this is a Prest-O-Lite compressed air cylinder intended to be able to inflate your tires out on the road. It would be recharged at your local dealer.