I have had bad experience's with I/O's and will never own another!!
That said if you had a I/O working and ready to go I would say stay with it till its time to re-power.
When you re-power the choice is yours! I/O or O/B depends what you are looking for?
IMO
Outboard, easy to replace, made to be on the water with less problems then I/O
But use more gas, in most cases nosier, and more to replace, if going new.
I/O cheaper on gas, quite, cheaper to replace.
But IMO they were never meant to be in a boat!! you are always working on them for one thing or the other! and I rather be fishing then working.
If you were to go new, the newer OB are much quieter, great on gas!! They are just as good if not better then a I/O.
Conversion is pretty easy if you decided to go that route.
First you have remove all the old parts, and don't throw any of it away!! Its worth its weight in Gold to the right people!! I sold all my IO parts for $1000
After that you need to plug the hole left behind. For that you go on the inside of the boat and you cut the inside liner and the plywood square (do not cut the out side glass!!!!) Now you want to cut just the first layer of ply only (3/4") about 1 or 2 inches bigger then the second layer.
Now take a new piece of ply the size of the first hole and coat with resin and cloth (make the cloth 2" bigger then the ply) paint the bare glass in the ole with resin and then put the ply in the hole, using the extra glass to glue to the wider cut ply.
Now take you 2nd ply and do the same thing and glue to the first ply you just put in the hole, again over lapping the glass by 3" to the inside liner.
Now cover the whole thing with glass till you are the same thickness as the inside liner.
Now go on the out side of the boat and fill the hole with matt and resin till its the same level as the outside glass. Sand smooth and gel coat or marine tex over the glass again sand.
Hole is now fixed and ready for you to install the bracket.
Go with a 25" shaft Out board and nothing less!! On the bracket go with the shortest set back that you can and still get the motor to tilt up off the ground.
Install bracket and motor and you are good to go!!
Theres more to it, and if you decided to do it we could get into it in more detail. but this gives you a general idea.
I never did it before and I had it done in 2 days!
Its up to you what you want to do!! But no matter what I believe you should start fresh with a outboard or new marine Motor.