I've never seen detailed specs from Yanmar, would love to if someone has them. Yanmar mounts have a part number and an 'ID'. The ID is the weight rating (in pounds I believe, go figure).
The 4JH5 with SD50
is specced from the factory (IIRC) with a set of ID 430 mounts. The ID should be embossed in the rubber on the side of the mount, so you may be able to check existing.