A couple small problems - Need advice

[MuscleStang351]

In response to the coolant overflow can, if you had it in place it would catch the overflowing coolant and when the system cooled down it would siphen back into the radiator, so when you replace it you should have no problem.

As for the fuel cap, your stock one should be or I should say the stock one is vented, and your system shouldnt build up too much pressure. So thats where I would start looking, the cap.
Good luck