The MX-55 has quite a different tape path, with different tension arms than the 5050. So those might require a different technique to mod them to ball bearings, can't say for sure. The only parts that look like they might easily fit would be the ball bearings in the tape guides between the heads, but again I can't say for sure that the stock MX-55 guides are the same as the ones in the MX-5050 without having an MX-55 to guide take apart. They do look very similar:
MX-55 guides
Modded MX-5050 guide
