This mod (moving nfb signal from one OT out to another, in this case from 8 Ohm to 4 Ohm) should work on literally any class AB push pull tube power amp with nfb (negative feedback).
Downside is, that your nfb controls (Deep and Presence) will have a little less effect. Which may or may not be a good thing, depends on your taste.
I found the Diezels I have had, and/or played to be too smooth and muffled.
Moving the nfb from 8 Ohm to 4 Ohm tap could be a good and simple mod, to up treble and high mids a little.
To tighten up the low end from the preamp gain side, this mod will not help, IMO. I think, using lower output, PAF type pickups help a lot (or increasing pickup distance to strings, can make a huge difference !).
IF I were to mod a Diezel for a tighter distortion, I'd rather change some of the mud-killing high passes early in the signal path. But tbh, the rather fat and muffled (or warm) base sound is a rather Diezel-specific sound quality, and if you don't like this, maye another amp is better for you?
