Looking at a YT359 and was told not from Yanmar. Was told WR Long supplies the kit, impression given me was they had at least working agreement with Yanmar on this. Dealer told me they had installed one and the amount of time it took them to me was rather longer than would have expected. Have a local tractor garage who installed a WR Long third function on nephews NH last year for lower price than I was given by the Yanmar dealership. "IF" memory is correct their price for the valve assembly itself was about what nephew paid for the valve assembly and installation. I do understand the price of the valve kit can vary with depending on the tractor.
Valve assembly think was told 1,100 to 1,200 for the Yt359 with no number for the installation.