From my experience, engines that came in B210/B310 are pretty reliable, and you can drive them continuously at highway speeds for long distances without any issues.
When the power is concerned, if the carb is tuned properly, these cars can keep up with newer cars without any issues. However, the brakes need to improve.
So, if you are going to buy a B210, do not go for an engine swap. Just get it fixed by a competent mechanic who is familiar with cars from this era.