Hi Norm

I've had a few mowers over the years that people had fitted bigger tyres over the original tyres ,that
increased the diameter , about 1/2 an inch of rubber would do to test the mower ,you could use tie wire
to hold some rubber to the outside of the original wheel to work out if you have the right size to increase
the drive speed that you are looking for ,then machine some tyres from old wheels to glue to the Honda
wheels ,I've would have wheels here you can use for tyres if you can't find any.

The first thing I would do is check the diameter of the original wheels as they may have worn down ,
they should be 8 inches .
https://www.ebay.com.au/itm/2-x-SET...er-hru214-hru215-and-hru216/201547830674

It would be worth checking the RPM .

Cheers
Max.