As of year..2017, they didn't make the Z-glides for the Z500, Z400, or Z300 series Ztraks. They may be available now. I still wouldn't buy them for my Z710A. I added a suspension seat with special adapter mechanism that I made, and it really did help my aching back.
I had a Z445 for eight years and loved it. I recently gave it to my brother as it still ran and operated perfect at 8 years and over 300 hours and purchased a new Z915E. IMHO the Z445 is enough lighter that the suspension wouldn't be able to take as much advantage of the suspension as the heavier mowers would.