I just completed installing a rear oil seal kit last month. Since you have the engine out of the car, now would be an excellent time to do it. The instructions say you can install it with the engine still in the car, but I wouldn't recommend it. Here are a couple of tips that might help.
1) The screws supplied with my kit were metric, rather than by a metric tap that I'm unlikely to use again, I went to the hardware store and found an identical screw in US thread(10-32). While your there, buy about six 1/8" drills
2)Enlarging the hole in the engine backplate was quite a task. I tried all kinds of saws, electric and air powered grinders, but they hardly touched it. Here's where all those drills come into play. After you scribe a line into the backplate useing the pattern supplied with the kit. Put the back plate into a vise ( a drill press would probably be best) and start drilling your way along the scribed line. Every time you begin to drill a new hole, try to get as close as you can to the previous hole. If you overlap the holes too much, the drill will suddenly slip into the adjacent hole and break. Eventually you will make it to the end. (About 1 hour) If your lucky, you will be able to break out the piece with a hammer, I had to use a saw in several places to get it out. Now get out your hand file and start smoothing out the edge. The work is very tedious, but it can be done in about 2 plus hours, including the drilling.
Go for it! Sky