When I got my Mercury 200, the previous owner had already converted it to premix, but he included the parts he took off.
I toyed around with converting it back, but the more research I did, the more that I noticed how much was written about failures and why the extra hassle along with idle fowling of premix was worth converting away from injection on the old systems with the plastic drive gear.
There was one highly recommended alternative suggestion, which I seriously considered if I wouldn't have to revise a portion of the cover because certain years where narrower, plus I used some of the critical space to install an electric primer off of a Sportjet engine to eliminate hand priming issues...besides, in the end I have gotten used to the premix again and worry about injection issues less.
So just for your consideration maybe some time in the future, the mentioned alternative was for an electric/electronic motor mixing system which is manufactured by a former Mercury person. Everything I looked up speaks very highly of his system as well as his knowledge, and he seems very attentive and hands on - he responded to my email about why my motor's year wasn't in the list in about 15-20 minutes and told me how to modify the cover if I wanted it to fit because that was the only obstacle for it working on that year motor. His website is:
www.marinesolutionswi.comGood luck.