Were it me and the 6 was in good shape and was installed correctly, I'd leave it and have a fine torque happy driver / worker. That said, I'm a HUGE FE fan and there's always room for a good FE.
In other words there's no wrong answer to this question, so do the "work sheet" thing and decide what works for ya
example
1) 240 or 300 (either is a FINE engine) and what's it's condition
2) What's the KNOWN condition of the 360? (IE how much $ needs to be spent on oil leaks, carb, etc)
3) What all will need to be sourced to make the swap (assuming the 6 is in good order, weigh against).
4) what's more important to you as far as milage, feel, etc?
Darlin 69 Ranger 390 4v, PS, DS II, disc front, 3G alternator, 67 mirror.