The TT has a Hicas ball joint where the NA has a rubber bushing. I had a hell of a time pressing the ball joint into the NA knuckle, it's possible that the hole is slightly (like .5mm) smaller on the NA.
The wheel bearing dust seal is a little larger for the TT. This is easy to swap.
Everything else is exactly the same (as close as I could measure). I swapped the knuckle from a 91NA to a 95TT. I'm talking about the knuckle itself -- obviously the bearing & other stuff that attaches to it are different.