The 15455 belt you took off is 45.5" long (the last 3 digits in 15455). And the 15415 is 41.5" long, 4" shorter than the 15455. Get one in between, like a 15435 or 15440.
Unless the working diameter of your alternator pulley is the same as your generator pulley, getting a belt for your '54 is a bit of a guessing game.
'57 GMC 102, Original 347 V8, HydraMatic, 3.08 rear gear, added A/C, disk front brakes, HEI, AFB carb, '98 Honda Black Currant paint. T-boned and totaled 10/12
'52 GMC 152 Stake Bed, Original 228, SM420, added A/C, HEI, disk front brakes, '67 Chev 3.55 rear gear. Gets used as a real truck.
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