Looking for some Insight in Dumble Steel String Singer Phase Inverter

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I have built an SSS style amp.  The only thing that was an issue was coming up with the inductor in the switchable filter.  The one HAD used is not around anymore, I think it was a Triad piece.  I used a 500mH Bourns piece with good results.  If you build one you are in for a real treat, if you really like a clean, glassy sounding amp.  Mine was 150 Watt with 4 x 6550's like he used.  I believe it was derived from a Winterland or a Dumbleland 300W.  SRV used a Winterland in Montrose at a mobile studio that Jackson Browne had there.  It was one that Jackson had stashed for his lap steel player.  Once SRV used it, he was spoiled and that is when he ordered one.  HAD later canceled his order though I read because SRV asked when it would be finished.

    After reading the Dumble chapter in TUT6 (if you don't have it get it!)  I got really interested in the different Dumble circuits. Most are simply variations of what is in TUT6  but the Steel String Singer caught my attention since it's a little different. Basically what I'm seeing is the Dumble clean channel but with a reverb configured a bit like standalone reverb unit and switchable filter.  That makes sense to me.  

However the topology of the phase inverter does not. It looks like a schmitt but has a cathode follower for each drive line.  Is there any benefit to this approach over the standard plate driven configuration? Has anyone here played an amp with this topology? I've attached a schematic!

Hmmm....I've having trouble  attaching  the PDF.  Hopefully you guys can still envision what I'm talking about....