It is pretty simple to support the engine with a small scissor jack and a small piece of plywood
under the jack and between the jack and the oil
You can then unbolt the brackets one at a time that sit on the mounts and swap out the mounts one at a time.
You should be able to keep the "settings" ie. turns on the threaded studs that go into the brackets fairly close and once all the mounts have been replaced, then call the $200 per hour mechanic
and just have him do the alignment.
If you are not "all thumbs", read up about aligning the flanges and get someone to help you adjust the mount heights and positions while you measure with the feeler gauge.
Be aware that Yanmar
mounts for 3GM30s are of two different hardnesses. If you need a shop manual that describes all this, I have a digital copy I can email
or I think the Yanmar
shop manual is posted on this website, somewhere.
I found Bay Shore to be quite reasonable with their parts
pricing, but changing engine mounts and aligning the flanges should take about 4 hours max.