heater core leak?

Hey everyone i need some help. So i have a 1976 Plymouth duster. It originally came with a slant six and A/C. now i have a 340 in it with no A/C. I need help because i went to go clean dirt off of my passenger side floor mat and it was soaking wet with radiator fluid. it looked like it was coming from the A/C box up under the dash even though there is no A/C hooked up. it might just be running down the side. I'll send some pictures if anyone can help. i know the heater core is bad because the defrosters do not work but the A/C blows air. Also, do i even need the A/C box? if i have to take it get to the heater core is it worth putting back in? am i allowed to take it out for good? if anyone has done this or knows I would really appreciate the help. thank you.

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