Heater or valve leak????? How to take it out????

I just took the heater box out of my 65...4 bolts on the fan motor retainer under the hood and two screws up thru the heater box on the inside and its out.
If you have the clips off and the front off there is 4 screws holding the core in..the hardest part with the box in the car will probably be the retainer on the outlet pipes, I don't know if you can get at it from under the dash without alot of swearing and bloody knuckles.