Please let me know how this goes. I too wish to replace the mounts on my 2GM in a 1983 Hunter 31.
I'm going to take some photos/measurements to make sure that those aftermarket motor mounts really match (I have my doubts).
Still confused why Yanmar has a different part numbers for front/back. Most likely, the rear mounts may be beefier because they have to support the transmission, but I'm just guessing.
Also, it IS necessary to re-align the drive shaft, which I have never done. I heard you disconnect the drive shaft flange, and tweak the engine mounts so all sides of the flange is aligned with the engine equally (as you turn the flange) within 4mm.
My engine DOES shake at low RPMs (500-600). But is this due to weak motor mounts, bad injector, bad valve? Is this common on a 2GM20F? Would replacing the mounts just be treating a symptom?
Maybe my mounts are fine. (see photo) They LOOK OK to me. It is obvious that the existing rubber is "stressed" due to the angle of engine mounting. The rear rubber is compressed while the front is stretched. Will the aftermarket mounts adapt to this angle?
How can you tell (for sure) that your motor mounts are bad, or do they just get soft and spongy over time? From what I can see, the rubber seems intact.
Also, if I replace the mounts with new ones, the shaking may reduce, but will this cause additional stress on the mounts/bolts/etc.
A lot to consider!
I may have to visit the good folks at Tacoma Diesel, as suggested earlier.