The old tanks and new tanks are all the same hight. The Model IV round cowl had the tank shortened due to the tight space of the cowl. It reduces the oil quantity a minuscule amount.
I want to use the new tank because it has an upgraded hose connection to A/N fittings and I like the fact that the inlet and outlet ports are on the lid. It makes identifying a crack or failure easy and and easier fix than pulling the tank.
It looks like I will need to get longer plug wires and sheaths to move the CDI but I agree, moving it is the only option for lifespan of the part. Here is a picture of the tank and you can see that I need to shorten the rest of the hardware associated with the tank.