Personally, no, I have not done this but anything is possible through the application of enough time and enough money. I am assuming the boat in question was originally an outboard? (the inboard engine was an available option, but most were outboards) I am also assuming that you are referring to a straight E25 and not the 25+ as they are two very different boats.
If it did have the inboard from the factory, it should be a relatively easy R&R. If not, then not, access will be an issue (I cut an access hatch in the bottom of my port side cockpit locker to get at my factory water tank (which would have to be moved) but its not big enough to get an engine in or out. Drilling for the shaft log and cutlass bearing will be critical as will the motor mount locations. Get them even slightly off and you will be plagued with vibration and excess wear issues from the get go.
Assuming again it was originally an outboard, one is prompted to ask why you would want to do this, an OMC 9.9 saildrive or the like is a perfect low profile motor for this boat and she handles as well or better than most inboards in sailboats of this size range. Also, most aftermarket modifications of this extensive scope could (and likely will) adversly effect the value of the vessel even if professionally done.
Check out Joe Williams' excellent E25 website at ericson25.com. I think the owner in Idaho has an inboard, they may be able to help you.
Best of Luck,
John