You can just trim up the input shaft and the bearing retainer a bit, and no need for an adapter. Which truck is this going in?
Here's the info from my swap. http://www.mongosgarage.com/tech/t5/index.htm
I've been told that the clutch disk's that we've used in the past that are listed there have been discontinued by O'Reilly and I haven't taken time to dig through my parts books to try to find another one that fits the specs. You need 14 Spline and it's hard to explain but you need a clutch disk with the center piece that slides on the splines is smaller on one side than the other in order to have enough room to disengage. The other option is to use a Di Grinder to extend the splines further back on the input shaft if you can't find a clutch with a shorter side.
Mongo

Mongo's Garage
Vintage GM Truck's & Parts
https://mongosgarage.com