What is the best way to get an overdrive auto in a 67 Barracuda?

To make the GV shift like lightning, I bypassed their little black box. I was very disappointed at the shift speed upon first installation. I mean, I paid all this money, and the thing sucked! So I tried it direct to 12v. POW! Holeeeey! I said, and the computer got the file13.Now if I shift it without the clutch, at WOT she barks the tires at 80mph with 295s. Under normal use I simultaneously hit the button and clutch it a little, to make it a little easier on the powertrain. But with the new split percents my rpm only drops 660rpm from 3000, so the shock is a little milder.....
With an automatic,the TC will absorb most of it.
I shift that GV under WOT without the clutch. And I only have to pull the stick one time at about the 4 or 5 second mark. The beauty of the 367 is, it only has maybe a little over 400ftlbs, so the tires can sorta keep up. That thing shifts faster and harder than anything else you can put into an A-body. Street295/50-15s, cannot keep up on the street spinning clear to past 80 mph. I have a 7000rpm shift limiter, and on a bad day, the engine is on it,all the way,non-stop; Well except for a few milliseconds at the aforementioned 4.5 second mark.I have 4.5 seconds to get ready to PULL! The other two shifts are electric, and since my car traps at 93 in the eighth,I have plenty of time to line those up. But it is close, about 2 seconds between shifts.It sounds like not much when you say it. But on the track it seems forever.