We had an old 36" Cub Cadet that had a two-blade, timed belt mower deck. It used a Gilmer belt, like the timing belt on cars now. Never had any problems with it and the belt never wore out, either.
This was a '60s vintage CC. Pontiac had the first toothed timing belt that I can remember, on an inline six cylinder engine that was used in the Tempest. It was in the '60s, too.