Brenden, if the blade uses an insert type rubber blade you can get the inserts at your local Walmart. They will be too long, but you can cut them and get two inserts for the price of one. I've done that using the same arm you are using.
its very narrow, any idea what year the arm is from? its for my Model A, the A has a Bosh 12 volt motor on it . I have seen a wiper arm like it before but I don't know where
Looks like the old British type, used on MGB's etc. Those are also the size used on 48-52 F-series. I bought replacement Trico blades at O'Reilly's, p/n TRI 33-101
Believe you are correct. This is the original wiper arm and replacement blade ( made to use two different arm configurations) on my '51 Merc.
12 inch replacement blade is Trico 33-122