How did you decide that you need new mounts ? My boat is an '84 and they are original. I get a fair bit of engine movement but how much is too much ? I pried up on the mounts and the rubber is still bonded to the metal.
Mine is a Yanmar 2 GM and the mounts from Yanmar are rather expensive. A mechanic told me that if I go for the more standard mount I will get a lot more vibration transferred to the boat.
Going to find another Yanmar 2 GM and see how much it moves.