When I did mine I had to drill the pin holding the old bushing in place and then pull it out. I tried various methods but ended up tapping two small holes in the old bushing and threading small screws into it and then using a puller. The original oil seal remained in the tube and was pushed farther in with the Okie assembly.
One thing you have to be very careful with is ensuring the metal chips from the drilling are cleaned out. I used a small magnet and compressed air. You don't want any metal debris in there when the Okie assembly goes in.
You should also lubricate the seal to help ensure that it won't leak.
For me it was a time consuming job and I don't want to do it again. Its been 3 years and about 5500 miles since I did it and I often crawl under the truck to check my transmission fluid level to make certain its not leaking past the seal. If it happens again I will go to an open drive line.
