Marvel Team-Up started in 1972 as a second Spider-Man title, dedicated to the webslinger, well, teaming up, with other Marvel superheroes. Issue #4 features our first proper appearance of the X-Men as a team since their cancellation (well, Bobby, Scott, Jean and Warren, anyway). Beast we'll see more of tomorrow. They team up (after a brief misunderstanding and fight) to take down Michael Morbius, who is stealing life force from other people to remain alive... That's about it.
Both of these are reprinted in Essential Classic X-Men vol 3, and are fairly generic guest appearances of the X-Men in other people's comics, much as had been happening before 1970. Neither stand to be analysed as X-Men stories disguised by being in someone else's title.