Something very odd there.  No sb220 excluded 80 meters.  That one must have 
been in the hands of a cb guy and modified.  Should work fine on A.M. I 
wouldn't push it past around 250 watts input.  Those tubes aren't cheap, and 
the signal gain isn't worth any risk.  You might get around 110 watts 
carrier out, which is 440 watts PEP.  Should do you well.  Some of the guys 
doing this might have better advice.  Mine is very conservative.
Hope to hear you on 1880 or 3985.  I'll fire up the valiant.