91 250x needs help

Greetings to all! Please forgive my lack of computer skills if this has been discussed, I could not find an answer. My son got a 91 250x and 2nd gear sounds like teeth are chipped, it came with a 2002 300ex motor with unknown problems besides a broken case Cover. Question is can I use tyranny parts from 300 to fix 250? Or any other combination of parts to make one good motor? Thank you.

91 250x needs help

Greetings to all! Please forgive my lack of computer skills if this has been discussed, I could not find an answer. My son got a 91 250x and 2nd gear sounds like teeth are chipped, it came with a 2002 300ex motor with unknown problems besides a broken case Cover. Question is can I use tyranny parts from 300 to fix 250? Or any other combination of parts to make one good motor? Thank you.