I should take the heater core repaired in our 72 roadrunnr, what's the easiest way to remove it?

First I would take off the heater hoses from the eng side firewall and replace em with some junk hoses and run some water thru the core to get all the antifreeze out to minimize the antifreeze mess on your inside parts/carpet (first put a thick towell under the box). Take the small thin plate/phillips screw that is on the firewall securing the nipples where they come thru the firewall (if it has one). On the inside I have no specific info I would just take off the cables and wires etc & possibly the glove box so you can work the heater box back & tilt it to let the nipples come thru the firewall

Drop the whole box out of the car.
With or w/o AC?

In addition to what Robert said, there are 4 or 5 bolts under the hood on the firewall that need taken off. There is a bolt on top of the heater box inside the car that needs undone, the vacuum hoses, a couple of electrical connectors, the cable from the heater/ac control panel. It is a lot easier if the front seat has been removed from the car.

Under the hood are the heater hoses and the a/c hoses if you have a/c. If you have a/c and it was working, you may want a shop to vacuum out the refrigerant.

When I do the heater cores, I replace the A/C evap too. It is such a chore to take out the box, the extra $350 for an evap core is worth it.

A lot easier if you remove the glove compartment first. For two reasons: (1) you can get to the cables/vacuum(if equipped)/electrical connector(s) easier because you can see what you're doing, and (2) you may need to wiggle the box forward some to have the heater nipples clear the firewall. Also, if A/C equipped, might be easier to remove the blower motor first to reduce the weight of the box that you have to manhandle. Even just the non-A/C box is bulky to move. Make sure you don't forget to loosen/unhook the hook that catches the top of the fresh air intake port inside the cowl. You can tell what it is by removing the passenger side cowl grille and reaching inside to the feel the hook at the aft side of the rim of the port. the bolt into the hook can be accessed through the fresh air door in the box above the passenger's side footwell (non-A/C box). Not sure if it's the same on the A/C box, but it still has the hook, IIRC.