Peterborough sold at least four different models of aluminum deck boats as part of its Admiral series. Your 185 is the smallest model of the four. There was also a 22-footer (Admiral 225), a 26-footer (Admiral 265, which had a standard hard overhead canopy that doubled as a sun pad) and a 30-footer (Admiral 300, a double-decker for almost its full length). Both the 26 and 30 could have a camper top option, so you could completely close them up and camp out for a few days in nice weather.
The Admirals were sold from 1984 until the Peterborough company was acquired by Alcan Group in 1990. Alcan had other ideas for the company, so 1989 is the last model year for these. All Admirals were fairly rectangular in shape, very stable, and just about bulletproof. There is a similar boat series built by Peterborough called the Sunliner, which was also sold in 18-, 22- and 26-foot versions. The Sunliner was basically the same thing as an Admiral, but was stripped down with fewer features and cheaper seats / carpet, so it could be sold at a lower price.
Both the Admiral and Sunliner boats have relatively low freeboard, so the 60 hp on your boat is probably close to max power. I can't find an actual max power rating for the 185, but according to my reference (an old catalogue) the 30-footer tops out at 175 hp, and the 26-footer is rated to a 150. If we work that backwards, the 22 would probably be somewhere around 115 hp, so your 185 likely tops off at around 75hp. It might be okay with a 90, but as each of these boats gets progressively narrower, as well as shorter, maybe not.
The biggest worry about putting on an engine that's over the boat's rated capacity is that if you ever have an accident, you're almost guaranteed to be sued. And, your insurance will not cover you if you're over capacity.
I'd suggest you contact Transport Canada's Office of Boating Safety at http://www.tc.gc.ca/eng/marinesafety/debs-obs-contactus-menu-2982.htm. They will have capacity plate records for every make and model of boat ever sold in this country. Or, try contacting Princecraft (http://www.princecraft.com/aluminum-boat/About-Princecraft/Contact-us.aspx). Princecraft bought Alcan many years ago, and would subsequently have old Peterborough records in their files.
My gut feel is you're probably fine to 70 - 75 hp. But, better to check before you plunk down a lot of cash on a new outboard.