I had a 23' hard top with a 350 Chev. I wanted to repower with an outboard but was convinced not to by the builder as the variation in weight would have required much work to maintain proper weight distribution and therefore boat trim.  It was deemed better to change the boat rather than potentially turning the existing boat into an ugly duckling.

Whatever you decide I would certainly seek assistance from a marine architect especially if its a 26 footer

cheers

 dont get one with a murcruiser inboard 

they are no good and you will have your hand in your pocket all the time 

 I have a 26 open,twin 190 hp mercruisers. One of the best all rounder boats I've been on. Not the fastest boat around but will do every thing you want. Ther was a TV show called hook line and sinker they did a project 25 carribean and put on a yammy 350.

 The beam on the 27 is to wide 3.1m and the 26 is 3.0 from memory and you will need a small truck to tow it legally, they weigh about 3100kg so over 4 ton with gear on the trailer.The hull runs a deep v and becomes very unstable with outboards as they like a lot of weight in the stern you would have to run with a lot of fuel and water to counteract.Carribean never built either model with out board option for those reasons the Bertram 25 was exactly the same though 2.9m beam  search the American website The Hull Truth you will find info on the yanks 25 bertys with out board conversion.I have converted two 25 Bertram's for a customers with 2x225 optimax mercs on a stepped pod relocated the fuel tanks to the stern and made the pod as a water tank for more weight. The other Berty was Twin 225 opti's on to the transom hulls are solid on these boats and run a fibreglass stringer  system which eliminates the issue of wood rot. If this is what you want I would advise to buy a 25 cheap with old inboards and do it up be prepared to open the wallet though and don't forget about resale.