Hy 1961mark, according to my Canadian parts book the following wheels were available for a 40 series in 1961. p/n 3729813 19.5"X5.5"
p/n 2364442 18"X5"
p/n 5769144 18"X5.5"
the 19.5" would be tubeless the 18"s would be tube type American trucks may be different, hope that helps.