The problem you are going to have....is the stock throttle grip housing most likely won't take a larger diameter throttle tube.   I don't know if you can shim the stock throttle tube in a way that will make it a larger diameter where the cable wraps around the tube.

The only other option(s) is to make the cam on the carb a smaller diameter if you are using the stock carb.......or change the throttle housing - which would also require you to use a different stop/starter switch.

I have a different throttle on my bike (7/8" bars), and it is a Magura Duo throttle.  It has a 1/4 turn side, and on the other side you can get a faster throttle.  These throttle are mostly used on racing or Off Road motorcycles.

http://www.ebay.com/itm/Magura-Duo-314-Throttle-Grips-Motocross-AHRMA-VMX-Hus...

I use the 1/4 side, and JOG is correct....it is harder to hold a steady cruise speed, as a small movement of the throttle makes a bigger change at the carb.....I suspect that is why most street bikes don't use 1/4 turn throttles.

It also requires more strength to turn....as the grip movement does more work as it moves, and this can get tiring on long rides.

A "crampbuster" works for me with a right wrist that has limited motion.  I can use the heel of my hand on long runs, or my thumb to add or change throttle settings .

Ok I'm going to try and say this without gagging & puking on my iPad.
Rev JOG you were right. The bike with stock throttle was hard to keep a constant speed/rpm on the highway and got worse with the one I modified so I put the stock one back on. I guess that mikuni vm36 carb and the carb upgrades I did gave it instant throttle response ,it's very touchy. Might try a lighter return spring in the carb. And exit speed isn't an issue with this beast,getting slowed down before the turn is. Anyway thanks for your opinion !