Please excuse dumb questions but, although I have had my Comanche for quite a while, I never seem to get much time to actually spend with it!

We are looking at an engine overhaul/replacement because, although still quite low time (just over 1000 hours), it was last overhauled in the early 70s! Performs pretty well and had a new carb not many hours ago but seems to be using oil recently. I would like to upgrade to fuel injection and understand that this is an approved option - what would I need to do from a paperwork perspective? My glass cockpit (birthday present from loving husband) has the necessary engine monitoring already.

Based in Europe but my toy is US registered.

It is approved on the Type Certificate Data Sheet which can be found on the FAA website. Off hand, you will need to remove the manual priming system and the fuel pumps used with the carbureted engine and install the fuel pump used with the fuel injected engine. The pump is not hard to find, but you might have to work to find the mounting brackets. That pump is installed under the copilot's foot well. A fuel flow gauge will be required unless your new system is certified as a primary replacement. If so, then all that is needed is the plumbing. A placard meeting the requirements of AD 2015-24-05 will be needed. AFM changes will be necessary. That is what I can think of off the top of my head.

Gillian,
I have a 61 250 and looked into this about 3 years ago. I was able to obtain two copies of 337 from airplanes that had the swap made. As Kristin said it must be done with the original parts per the type certificate. Dave Pratt of Aviation Performance Products has done a bunch of these as well
It was about 6-7 k in parts for the swap. A fuel servo, injectors, electric fuel pump, mechanical fuel pump, fuel flow gauge , fuel divider and associated lines. Clamps and hardware for the electric pump that Kristin mentioned under the co pilot side. And you may or may not need a new plenum for alternate air depending on your regulations. Make sure your cylinders have the hole machined for the injectors. Two of mine had the boss but had never been machined and plugged. And then there's labor. Dave probaly has a good idea, but I'd guess 3 k in labor .
Now after all that what are your benefits ? Sure your going to run a bit smother, but my carbed 540 still gets egt's around 150 of each other, and a dynamic propeller balance makes it very smooth. Fuel savings might be .5 per hour. Then of course you can't get carb ice. So the question is it worth the cost? While a fun project and definitly kool to have to me it was not
I have a engine monitor with a carb temp probe and will run partial carb heat to bring it to the 55 degree range. This better atomizes the fuel and won't allow any ice build up. The carb system is simple, and has been trouble free so I'm opting to spend the money on fuel instead. I use fine wire plugs which makes a huge difference in smoothness and no fouling issues. Good luck and let us know how it goes. If you'd like I can send you the copies of the 337 that I have.
Andrew

Thank you. That is actually an option I hadn't considered!

My thought was to replace the engine completely with an injected model. The current engine is quite smooth and the new carb did wonders for the fuel consumption but it is a little elderly.

Andrew - copies of the 337 would make an interesting read if you have them electronically?