5 speed hub spacing is almost always(over 90%) 120mm, which is the same as modern track hubs. So you would be able to swap out a track wheel.
The walmart bike would take a decent amount of work to get rolling, and you would have to swap out a few thing to get it riding comfortable, and then quickly swap out parts. In a short period of time you would have swapped out enough to pay for a better new bike, and soon enough you would have swapped out everything but the low end frame. It would be a money pit.