The OEM belt size for my Murray 42" deck riding mower is 37x75. Will it be a problem if I place a 37x88 belt on it?

37X75 is 1/2 x 88 1/4
37X88 is 1/2 X 91 1/4
their the same width . Ones longer
the pulleys are set up for a 1/2 inch belt .
if you put a wider belt it will not ride on the pulley properly.
Luck.