Tranny upgrade

You can pretty much just swap out the input shaft to fine spline and any reputable manual transmission shop can handle that. Get a hold of Walt at ProMotion and he can get the parts to you. 888.380.3670

They say he usually doesn't like to sell this stuff, but he will. He will try to talk you into a Tremec TKO600 swap. Don't let him.

For the price of upgrading your 3650, you may want to look into a TKO 500 or 600... If I remember correctly, the 3650 is rated at 360ft lbs... Typically the 10 spline input is the weak link so you can just have that replaced... since you need a new clutch disk anyways... any more digging through the gears and such, you are looking at some serious costs thus the suggestion to get a different transmission. 6 speed would be cool but your end gear ratio will be similar to what you have now so not real savings on the freeway if that was your objective. What the t56 adds is a .8 5th gear.
Kevin

Maybe look into a TR6060 (GT500 6 speed) swap for double overdrive. It can handle the power and D&D sells a complete kit.