still doesn't add up: if you use 52" as actual diameter, then 60mph @
0.85=2214 rpm, 0.79=2058, 0.75=1954, and 0.73=1902.
if you use 53", then
0.85=2173 rpm, 0.79=2019, 0.75=1917, and 0.73=1866
so, either you have the rare -B model trans with the 0.73 OD (which is possible) or your tach is...