Are you sure it is not a 1500? Pictures maybe? After reading back through this old thread I see it could be a 150. No doubt a rare one if it truly is. Have you read through the entire thread?
This was just posted in Atl.CL. Farm and garden a few days ago. If it is a 150 this 146 almost has to be vary similar. May want to try and reply and check for any info on it that can be useful... YANMAR YM146 lawn tractor - farm & garden - by owner - sale