Initially, the V67G had the same insides as the 2001. Brent Casey speced a new transformer for the V67G which eliminated the ringing problem of the 2001's transformer, and changed to some new transistors and caps which lowered the self noise a bit.
When I tested them, I didn't like the harsh top end of the 2001, but I found the V67G to be a great sounding mic, at least in my opinion.
One of the biggest reasons for the difference in sound is the shape of the housing and the grill, which influences the sound considerably above 5kHz. The sound of the V67G is VERY different than the 2001, even though they share a lot of the same components.
AFAIK, the 2001 still uses the original transformer, and all the various V67 models use the better transformers.
"Voicing" a mic is not an easy task. When Stephan Sank modified
my Beyer M260 ribbon mic, we spent about 30 minutes just adjusting the ribbon tension to get it to sound "right".
When we put the ball end back on the mic, the sound changed dramatically, and we spent another 1/2 hour tracking it down to where we finally determined the change was caused by the Beyer gauze inside the ball. We switched to the RCA silk, and the problem disappeared.
The things that are very near the capsule can make a very big difference in the sound. High frequencies are very directional and diffraction, reflection, absorbtion, and resonances all come into play when you're dealing with objects within an inch of a capsule's diaphragm.