Re: 24 volt
A few years back ARRL had a PA contesting aiming for 40 watts or so. Perhaps you are referring to the design by NM0S? I can't find the schematic on the web - so this is little help to folk outside US that likely don't belong to ARRL (I wish they would make articles open source after 1 year !)
Here are some comments on it --
Please note some designs are optimized or configured for C -- careful bias adjustment is needed (as in the ubitx) for SSB linearity.
On the ubitx - given expense of making a full set of 40 watt low pass filters - perhaps consider building a PA for just 2 or 3 bands - where you may 'need' QRO.
My first advice on the BITX and uBITX -- enjoy it some as is! 5 watts on 40m SSB can cross oceans when the bands allow.