Well, luckily I will not be overspeeding my driveshaft. It has a critical speed the way it sits of about 10,000 rpm and if shortened for an overdrive, would go to over 12,000 rpm+.(3.5" Aluminum MMC).
That Granada is from Ireland and has a top speed of more then 188 mph. That's just what he did in the standing mile from a dead stop to a 1 mile marker. If he did not run into belt issues I am sure he would have been real close to 200 mph. Pretty good for a 3600 lb barn door either way!
Boy, sounds like the 4l80 might handle the power, but would need 5k invested to last. I would be real worried about a stock trans and how it would last for the time being. A T56 setup will not cost a thing if I trade my current setup even up for one, but I have to rebuild it once a year with real heavy beatings. I will also take much more time for a swap. I already have a pedal set, but will need to do some tunnel work and get the clutch setup installed and working correctly. Plus, my wife can't drive stick, so that is another bad factor.
I guess I will keep looking into both options for now and try to make a choice sooner or later.
Thanks for all the input.