Tom the replacement of the heater core in my 74 Hornet's is as you said for your 70. In my opinion it was easy. From start to finish it took me an hour and I am an old cripple. You should see what you have to do to change a heater core in a modern car or truck. I'll pass and keep my old Hornet's. The heater core was one of the first things I replaced on my orange Hornet when I bought it. The previous owner had it bypassed. I also replaced the heater control valve with a modern replacement. 74's had a vacuum controlled one, what did the 70 have? "Doc"