Welcome aboard Old Timer! I'm no spring chicken at 60 plus a few and I hope I'm still in the saddle at your age! A have a Magician and I have thought a lot about the sprocket. It is the weak area of this bike and it needs a 40 rear badly so I hope you can figure it out. It's gonna be close given the design. Rather than do it yourself I would suggest you contact these people and see if they can make you one. For the money I do not think you can beat it. Something I was gonna do I have not gotten around to. Let us know how it works out.
https://shop.pbisprockets.com/