Office of Steam Forum for Model & Toy Steam Gas & Hot Air Engines

Yes and no!

The #75 has holes in the firebox to allow for draft for the flames. The #70's boiler has a heater blanket and asbestos sheets under that, which certainly should not be exposed to any open flame. I don't think this is the way you want to go about making both units operational.

Now if you are just talking about switching each entire boiler system to use with the same engine unit, then yes, they may be interchangeable in that manner, provided the mount spacings are compatible.