Hi Ewan,
Depending on whether SPA type belts are ok to use with Clutching/Idler pulleys which may be a cause of belt deterioration?,
the SPA 732 belt (732mm) is sold as the INSIDE dimension (28.82 inches).
Wheel Horse belts are/were measured around the Outer circumference, so a 732 will be greater than 29 inches.
Presuming your replacement Pulleys are the same (Pitch) size as originals, and the distance apart is the same, then the belt should be ok.
Snatched this off the Web as an example-
Regards