I would think that age and condition of the mounts should be the reason for their replacement.
Hard to say without seeing them or having more info (oil soaked, split, cracked....)
If they do indeed require replacement, I would opt for nothing other than factory originals, price be damned.
Stiffer mounts will make for a lot more vibration through the boat, not too mention the additional forces they will transmit to the engine bed/hull.
There is only one thing worse than unhappy consequence caused by a repair and that is having the added pleasure of paying for the exercise
We have the PYI PSS seal and love it, far superior to the Dripless it replaced.
No mounts were harmed or replaced during the conversion.