I havent done it to a Cessna yet but have changed out several IO-520's for the IO-550 in Bonanzas and the owners love it.  only problem they have is they have trouble keeping the speed down as 75 % power yeilds a high cruise speed ---right up to the airframe redline.
let us know how it works.  I have a friend who has an A185E that I will suggest this change when it comes time for the engine overhaul.

I have engine parts for a Continental IO-520 Cessa 185, IF anybody is looking......its been at the bottom of the lake for over 25 years,but still in ok shape......

I am interested in your IO520 engine parts. Also have a 75 C185 project for sale if you know of anyone looking.

I have about 200 hours on my IO550 in a 185.  I would do it again in a heartbeat.  Cost was about $10k more installed than a reman 520, but I think it adds that much to the value of the plane.  Smooth, lots more torque, trouble free.  I run lean of peak all the time.....full throttle, control power with mixture.  I don't pull the throttle back until setting up for approach.

YOu will see the same gains on floats too.  My airspeed is up....water runs shorter by about 5 seconds.  Big leap for you from a 470 to a 550....I went from a 520 to the 550 and am super impressed.  What do you think of the MT?  I have the 80" Hartzell wide chord and really like it.  Others swear by their big Macs....

Have you tried coming over to the dark side....running LOP?

The MT IS light....I've pulled the prop through on a friends plane....and really felt the difference.  Light is good on the nose of a 185....mine, at least, tends to be nose heavy as it is.

Regarding LOP, if you haven't discovered John Deakins Pelicans Perch articles, he seems to be the most knowledgable of anybody...great articles on engine management plus other fascinating stuff like flying a Hurricane, flying for Air America.......

Cheers, enjoy the 550!