Since no one else has chimed in... About ten years ago or so I put one in my 67 coupe. C4 and 3.55 gears. Fits nice, pretty much bullet proof. The OD unit can handle up to 1000 ft/lbs!
Shortened drive shaft, reworked exhaust (had an x-pipe that had to be moved rearward). Place for the manual shift button. Place to mount the auto/man switch. All in all a nice unit.
Just that it didn't pull the rpm's down enough for my liking. I wanted more reduction in rpm's. Thus, years later I put in a T-56. I still have the GV unit. I'd like to install in my 67 F-250....Just a different adapter. But the unit itself transfers over.
Being abroad, I would choose the one with cheaper access to services. Like I said though, the GV unit is virtually bulletproof. Not one problem in over four years of service.
With enough practice, it did sound bad ass ripping thru 1lo, 1hi, 2lo, 2hi and not even be breaking the fwy speed limit.
Get a ratchet shifter, as the stock shifter isn't friendly to banging the gears. It likes to slide into D when doing the 1hi 2lo shift. As well a micro switch. (at the time, they just had the hi beam type switch on the floor to shift manually)
Hope this helps. Just ask away if you need more answers.
Personally, I love my GV unit. Had similar issues with my X-pipe and so on but once everything was sorted out, it has been a blast. I use the foot control along with my magnum grip Street Bandit shifter and it has become one of my favorite things about the car. There is a bit of a learning curve but once you get used to it, it is awesome. It's true it doesn't drop freeway rpms drastically, but it's enough that I can easily cruise 85 with 3.70 gears. If I remember correctly, it dropped about 700 to 900 rpm off the top end. Let me just say that splitting gears is the $hit and even though the unit is expensive as hell, the fun makes it completely worth it!