We do not have a conversion kit for running biodiesel. Here are some links to information from Kubota regarding using biodiesel in their engines.
http://www.kubotaengine.com/support/fuel-and-motor-oil/biodiesel-statement http://www.kubotaengine.com/assets/documents/KEI-162.pdfIn particular, they mention that cold weather conditions can lead to fuel system plugging, hard starting, and other possible failures. Plugging can include both fuel filters and fuel lines. Additionally, microbial contamination and growth can contaminate and even corrode the fuel system when running biodiesel in engines. These are general considerations when dealing with biodiesel even as low as B5.
For B20, one thing to note from the second link (the PDF) is the chart showing fuel pumps and gaskets that may need to be changed. This is a table on page 2. When viewing the engine series, our T412/T618 machines are engine series SM, the T500s are engine series 05, and the T630/T900 is engine series V3.
I hope this helps. Let us know if not. Thanks!