Have you clarified which mouints are broken, the upper or the lower? The lower is usually OK and readily available but it’s the upper mount, on the front of the block, which can be hard to find intact and uually expensive when you do.
I’ve had a couple shaky 9.5’s where the problem was the bolts holding the lower mount onto the exhaust housing had worked their way loose. Tightening them back up helped get rid of the shakes. Hard to remember but I think I turned the motor upside down and reached them with a wrench. The upper mount is a different story as they like to separate. I have fixed one or two by using crazy glue on the pieces and clamping them overnight. The rubber and the plate must be thouroughly degreased and clean before the glue will work though. It’s usually the upper which goes and when it does, the motor will shake like a wet dog. And yeah, if you can work on an old Merc, you won’t have any trouble removing the side covers for access.
A good upper is worth its weight in gold and that’s why I have one squirrled away somewhere. In fact, I hid it so good I don’t even know where it is!
EDIT: Seem to be getting random photos again while posting. The thumbnail is correct.
