I can confidently say no 3 cylinder 50s. only 55,60,65,70.75.
They briefly made a 4 cylinder 50 in 58,59,60. also made a 4 cylinder 50 in 43,46 and 49.
I wonder perhaps if that 3 cylinder isn't something supplied by Suzuki.
As I understand it the 48spl was a bargin basement model based on the 2 cylinder 50.