GV Under/Overdrive Units

I'm currently running 3:55 gears and with this unit, it will ride like it had 2:76 gears. I'm considering going with 4:10s which will ride like I had 3:23 gears. I understand the unit is running at about $2800US plus shipping (over $3100CDN these days) and with some modification to the drive shaft, would give me 4 additional gear settings including a .78 final drive. Seems a lot cheaper than a new transmission accomplishing the same final result assuming you won't have to rebuild your A833.