It depends on who built the transmission and what modifications were performed. Some builders replace the factory TCC apply valve and spring with a special non-lock up sleeve that'll need to be removed.
In lieu of that, sometimes the spring is merely moved from the top of the TCC valve to the bottom to hold it in the 'applied' position. If that's the case, it'll need to be swapped back.
You'll also need to make sure that you've got an internal wiring harness, solenoid and valve body pressure switches. This stuff may or may not have been removed.
When you pull the NLU converter off, make sure that no one hacked off the little ground journal on the end of the input shaft (where the o-ring goes). Some aftermarket NLU converter configurations required that to be removed but a lock-up conveterter won't work properly without it.
