After searching I found a intake adapter for the ct3- with an aftermarket Mikuni 24vm-512. There have been a few threads that talk about getting this connection made. I am just sharing some info. The adapter is "Rubber Flange Adapter 35mm ID 2 inch center to center bolt holes" on ebay. I had to drill a small amount at the mounting holes to fit the 8mm bolts.

I have a CT1 but taking it you’re replacing a bolt on Mikuni with a rubber intake flange and associated carb like newer DTs. Is that correct? Unbolting the carb endless times for servicing is a pain. You have my attention! 

The carb that was on the bike had been left out without a filter or any other cover. There was a nest and dirt bridge over the whole carb. The needle was jammed and bent so off with that and I ended up with a Mikuni 24m-512 spigot carb. It was a hassle finding a flange adapter as I wanted to keep the intake that bolted up to the reed block. My first mistake was trying to fit a modern carb with a flange back on the old. It was too small so off to ebay . My second mistake was thinking any old flange could be adapted, and the one I got could not be used as needed. That is why I posted this info. We should learn from our mistakes so I decided to share the good news.