In my opinion, I would go get your MEL in a regular twin at a school like ATP or something. take a week at a time and punch it out. Then find out what the insurance needs to fly your Skymaster. Most of the time it might only require a mentor time to get enough hours to be on your own as PIC. Then you have a full Multi Engine certificate that gives you lots of options down the road.
https://www.skywarriorinc.com/multi-engine
https://www.faaflightschools.com/pennsylvania/
Lots of guys say they will never fly anything but a Skymaster so it's a waste of money and time. Well with the lack of Skymaster CFI's and DPE's I have to say that it's really the most logical choice. Also if you go somewhere away from home base and can just focus on training and not day to day interruptions it will be a much more useful situation.