I just a 2x12 Glaswerks loaded with 2 EVL's the cab is wired for 4ohms
I have one option and that is to rewire to 16ohms. I guess the tradition with D type amps
is running 4ohms. The reason Dumble originally did that is because he was sourcing Fender Twin transformers for his original Dumbles
but is there a tone advantage to running 4 ohms? I Googled it and one post said there is more low end at 4 and as you go up to 16 your getting more high end which is fine because the EV's are pretty
dark.

You definitely will notice a difference when you play on loud gig level.
4 ohm will be cleaner (more headroom), more hghs, punchier and louder.
16 ohm – darker, more compressed, not so loud.
It would be a good idea to install a switch on the cab which changes the cab resistance when needed.

Hey Burst, maybe you could contact Dave at Avatar Speakers and ask him for one of his jack harnesses.  It has 3 outputs, both speakers in parallel for 16 ohm, both speakers in series for 4 ohms, or either speaker at 8 ohms (assuming the EV's are of the 8 ohm variety, which is standard).  With this, you can simply switch the speaker cable between the jacks, being careful to make sure the amp is set to the correct impedance, or even run two amps through the cab, one through each speaker.  They work well, had one on my previous Avatar cab.

http://www.avatarspeakers.com/

Found it thanks!