Yes it was necessary to ensure you have full adjustability down to the last thread on the tie-rod. There isn't a lot of room for adjustability with the tie rod ends because the point where the threads start on the STi tie-rods are further out than on the LGT.
I sourced mine from a wrecked STi whose parts were on ebay . It came with the STi u-joint too!
The most difficult part for me was bleeding the system. It took me a number of tries to get all of the air out of the system. At first I did my best to bleed the system without the motor on. Once I got all of the air out that I could, I turned the car on and the fluid started to "froth". I checked all the connections for leaks and there were none. I had to turn the car on and off a number of times to bleed the system and allow the "froth" to dissipate. After the froth was gone, I drove it around and the system continued to bleed air as I drove around the block.
The second difficult part, which wasn't so difficult... Do make sure you center your steering wheel before you pull off the old steering rack, and keep it centered at all times. Also, be sure to center the new steering rack before installation. Mating it up with the U-joint and ensuring both the steering wheel and rack are centered will be a slight challenge.