While I am sure that you are going to get a lot of advise on this issues, I think you will find that anyone that has ever been to one of the Yanmar classes will advise you to ONLY purchase the OEM mounts.
The are very different for many of the Yanmar motors. Some have different mount fore/aft, and other actually have different mounts on all four corners (so I am told). I think you will find that the Yanmar mounts are about $100 each.
We actually had an incident where someone installed a new 2GM in a Hunter 30, the company that installed the engine reversered the forward and aft mounts and the engine shook so bad that it disconnected the shaft from the transmission. The owners had a Yanmar guy out and he swapped the mounts and everything was just fine.
Good luck!