peavey heritage vtx mods

So here's what I'm planning to do with the VTX, referring to the schematics I linked before. Power amp: I will keep the existing 4x6L6 tubes, their power supply, and the output transformer. Peavey has the 6L6 tubes connected to a very peculiar circuit, which I haven't seen anywhere else.  The grids, where audio signal usually comes in, are simply hooked to a DC bias voltage, no signal.  The signal (two mirrored phases) comes in to a totem-pole of power transistors, which modulate the current through the cathodes of the tubes, two pairs in push-pull.  It looks to me like they started with a purely solid state power amp, and then tacked on the tubes to increase the voltage swing and thus output power.  Clever, innovative, but no thank you! Instead, I will hope and assume that there's enough leeway in the rather beefy power transformer to handle two additional 12AX7 tubes (the issue is the heater currents).  One of these will be used as a conventional phase invert...

Here are links to the relevant schematics.  My upcoming discussion will refer to these. https://schematicheaven.net/newamps/peavey_heritage_vtx.pdf https://schematicheaven.net/fenderamps/deluxe_reverb_ab763_schem.pdf  

(This image is from reverb.com, but it's very similar to my unit -- even down to the missing "Peavey" logo!) So I have this interesting/strange Peavey amp, the Heritage VTX 130.  It's a 2x12 combo, with 4x6L6 power tubes (in a very strange configuration), along with a typical-for-Peavey-at-the-time solid state preamp (lots of coloured plastic knobs).  I got this thing for free, one of the 12" speakers has always been blown, but it still works pretty well, except of course funky, not-very-inspiring tone.  But given the tube output section, I've held on to it, always figuring that I'd make something out of it someday without having much of a plan of exactly what, or how.  Should I just replace the blown speaker?  Or cannibalize it for parts?  Or something in between? But now that I'm starting to plan how to put electric bass, and electric cello, into the music, I'm thinking to use this as a bass amp.  But with a little more effort than I was origina...