I think that most RIBs in this size can take 80/90hp, weight and it's distrabution might well be a factor however. I had a BWM 17 with an ageing Yam 80 2 stroke on the back, I replaced this with a Merc 4 Stroke which was much heavier. It did have the advantage of keeping the bow higher during normal use (something I wanted) however on jumps she would always land stern heavy.
From an insurance point of view, get in contact with Zodiac and ask them to confirm what size (HP and weight) of outboard is suitable for your model of RIB and if confirmed is OK then ask them for a new plaque. Manufacturers are always changing the lay up of hulls and improving upon materials used in construction. This would change the size and rating of which engine they use on the back.
Looks Slow but is Fast
Member of the ebay Blue RIB cover club.