Tim is correct, start with a #75 that way your not needlessly paying for a heater you don't intend to use & you won't have to gut all those components out of the firebox, you can always add a Jensen #15 generator to the plant. As Tim said...the Jensen #25 & the Jensen #75 are the exact same plant...the #75 minus the electric heater & cord.
Good luck with your project & please keep us informed of your progress .😊