Cool thread. I did this conversion years ago after I sent the spider gears flying in my old 7 1/4.
I did not know there was a difference in the housing types. I guess I had some dumb luck when ordering parts as the set of 3.55 gears and sure grip fit just fine in my 8 1/4. I was not sure what car it came out of as some guy gave it to me. It has 11 x 2in drums on it and it was impossible to find replacement parts. Couldn't keep tires on the car afterward....