Mnem... It's hard to know without a 1955 twin lead only usa cable mount socket - the surplus sales socket will need a bit of bodge-ing - it looks too big as is but it is closer than I have at present.
Well, it's easy enough in person to measure the diameter of the socket in your front panel, and while you're there with a straightedge, determine if the blades are centered in the cavity or offset. If it's ~20mm and the blades are offset from center, then you pretty much need a US AC extension cord like the one on the left. This you can easily carve down to fit safely in pretty much any socket of this type, BTW.
Alternately, you may be able to find one of these SJO 2-Wire NEMA 1-15P Power Tool Quick Lock Cords. IIRC, the twist-lock is easily cut off leaving a 2-wire socket pretty much perfect for this. Back in the day, canister vacuum cleaners had a cord with a similar rectangular molded rubber end that was approximately 1/8" larger than the two blade sockets themselves. They outlawed these ages ago, though.
Looking at that one from Surplus Sales, I expect that unless it fits correctly exactly the way it comes, you're not going to be able to grind it down without destroying it as a connector due to the way they assemble.
Good hunting,
mnem
*toddling off to ded*