Dyna seats interchange with other Dynas except for the Wide Glide, which is unique. They don't fit Softails or touring bikes.
Softail seats fit only Softails, and won't fit Dynas or Touring bikes. I think the Deuce is like the WG in that it is unique because of the rear frame/tire width, but not sure.
Touring seats fit all touring bikes if the console is the right length. The Tongue length varies to match the length of the tank console on touring seats. Road Kings have longer consoles and shorter tongues on their seats. But, you can use a road Glide or Electra glide seat on an RK if you use a shorter tank console. And, RoadKing seats will fit an EG or RG if you use a filler piece between their shorter console and short tongue on the RK seat.
HD has three families of frames for the TC88 motor, which determine largely seat fitment, with subcategories for console and tank length within each frame family; l Touring, Softail, and Dyna.