I tried the mag wheel cleaner on my transmission/bell housing as well. It did clean up the bell housing nicely, and I used a drill mounted wire brush on the transmission. I then sprayed it all with VHT sp145 engine paint clear coat, which is good to 550 degrees.
A word of caution, don’t get the wheel cleaner acid on the release bearing. It makes it sound really bad, and you will have to change it fairly soon after you put it all together. Guess how I know this?