I'm with Don, I've run original 235's and 283's thousands of highway miles on unleaded without problems .... this has been discussed to death here, these old low compression, low power stovebolts will run fine on unleaded fuel until something else creates the need for a rebuild if you don't abuse them - if you have the engine torn down and are rebuilding, not a big deal to do the seats, but there's no need to pull things apart just for that, and if you decide to pinch the pennies and don't do them on a rebuild, the engine will still last your lifetime for the easy use it'll get as a toy
Bill
