The other thing to consider is that having your prop just in front of your rudder is a big pplus. That is where your inboard engine puts it. Swinging an outboard way back over the transom means you will loose a lot of manuevarability at slower speed in marinas and such, and with the amount of windage that a sailboat offers (even without the sails up), manuevarability is a very good thing indeed to have!
My advice would be to get a porper assesment of the inboard and if at all possible, have it repaired/rebuilt.
Outboards are also louder, moresuseptible to being swamped by following seas and FAR FAR more suseptible to theft (with an inboard they just have to steal the whole boat). So unless you fancy hoisting a 25hp outboard in and out of your companionway everytime you want to get off the boat for a while, an inboard justifies itself nicely (the abilty to do maintenance at sea without having to hoist the engine inside or hang off the transom trying to swap a clogged filter) is also a big plus.
If you have a Yanmar diesel, I would especially advise making all effort to "save" it, as diesel is a far safer and more efficient fuel source for boats (1 litre of diesel takes you the same distance as about 3 litres of gas, so you do not need to carry as much).
Anyway, the C27 is a nice little boat, don't screw with it too much before you have had a chance to really use it and make a list of what you want to do to personalise it/optimise it to your needs and you will be fine.