54 chevy heater core

Hello all,
I have a 1954 chevy belair,I am trying to replace the heater core but having trouble.I don't know how to get it out.Has anyone replaced their heater core that can help me? I dont know how to open up the heater box.Also while I am in there i will replace the heater fan as well.Any help would be appreciated thank you in advance
Ty

 

The heater box connects to the ducting from the blower with four screws. Just disconnect the hoses and vent cables, pull those screws and also two bolts on the firewall and the whole heater box and core will fall on out. Its pretty simple to get out, puttin it back together is a pain.