Unless you want a driveline that clicks all the time and has lots of slop and is a heavy sob go ahead and use 2" and 2.5". If you want one that fits very snug and is a bit lighter yet still bomb proof use 2x.25 for the outer and 1.5x.25 for the inner and grind a space for the seam in the 1.5". Been beating on my square shaft for years not a single issue and it isn't so fawking annoying to listen to.
