dart rear seat swap need help

i have a 74 dart swinger and i obtained a good back seat from a 72 four door dart....the tabs at the bottom are not lining up where it bolts to the floor, any suggestions? im going to make it work regardless just didnt know if there were any tips ...also stoked that i found my broadcast sheet in ok shape hidden behind my factory seat! ALSO what is the best way to remove my heater core...top screws are near impossible to get to seems like you almost have to remove whole dash? idk hope not....also have to remove the smaller ac box under dash.....i am new here but i have a lot of work to do on my dart so any help or tips will be greatly appreciated thank you!