I believe they would have label it as a BB if it was a hex belt. And according to the IPL all the idlers are Flat type and only the spindle pulleys and the pulley at the engine are V type.
Now for the 5/8 x 177 here is a few possibles.
- Hustler 797720
- Oregon 15-019
- Stens 265-711
- Rotary 12322
- Toro/Exmark 114-8154
- PIX P-797720
Check out Amazon for some others based on these PNs. Those listed above all have list prices in the same ballpark as the Kubota one but a few aftermarkets on Amazon are about half that.
Meanwhile I am going the grocery store and hope I have a little left over for fuel.