You have a drive saver disc between the two coupling flanges. After unbolting the rear (aft) flange from the drive saver disc rotate and wiggle the shaft rearward and see how much clearance you get. Hopefully enough. I used a tire iron with two bolts protruding to hold the shaft from turning while removing the drive saver disc. After removal of the disc you can access the large coupling nut. I forget the size, Been a few years since I did mine. Best to use a 3/4" breaker bar with a 3 ft pipe over it for a cheater to break it loose. Remove the flat washer under the nut and then wiggle the coupling off the splines. Pry out the old seal and wipe out bore till clean with a rag. Spread a light coat of permatex or your choice of sealer on outside of new seal and tap it into the bore. Make sure to face the lip of the new seal facing fwd. Lube the coupling where it rides in the seal with some oil or grease. Check the coupling for wear on the seal area. If it's badly worn you can relocate the seal in or out a little bit so it rides in a different area of the hub. Do this before insalling seal. If hub is badly damaged replace it. Also use a new nut. Tighten the **** out of the nut or it will come loose and you will have to do the job again. I had to chainfall the trans up to get clearance to do mine. whole job takes about 2 hours. Good luck.