Which steps are required to replace the evaporator, after the a/c system has been emptied of refrigerant?
I suspect it's going to be a time-consuming job but it's necessary.

The car has been compressor-less for at least a year and I don't know if how it failed, so I'm replacing the a/c system components, in the hope of having A/C this summer.

Can the heater core be replaced without removing the evaporator or would now, when I will be replacing the evaporator, be the time to replace the heater core?

I'll be getting hold of a factory service manual in the near future but wish I had one now.

I will answer my own question for the benefit of others.

Yes, the heater core can be (and is) replaced without removing the evaporator. The evaporator is removed through the engine compartment. The heater core is removed from inside the car.

Secondly, what makes replacing the evaporator a PITA is the fact that after you remove all of the screws and bolts from the cover in the engine compartment , plus the blower, the bracket on the back of the engine, the relay center fuse block, vacuum tank, heat shield and the big suspension strut that blocks your way, you discover that some very sadistic engineers at GM decided to put ONE bolt that secures the cover INSIDE the vehicle.
Getting to the bolt requires removing the panels beneath the dash, the flexible accordion-like piece that connects the underdash vents to the floor vents, the lower console cover and the electronic brake control module and the brake module bracket which is secured to the firewall and is covering the freakin bolt that you need to get to.
GM colored this bolt shiny silver--but doesn't bother to mention this or the location of this bolt in their service manual.

I could not believe the huge buildup of not only grime but also a giant pile of pine needles and other debris that piled itself against the evaporator in the corner nearest the accumulator.

Though it is a real pain in the neck job, I am glad that I decided to replace the evaporator along with the other ac parts I replaced.

thanks for the post, i have often wondered what was involved in replacing evap and/or heater core. i am filing your report for future reference.

Gmman, I'm glad you've found the info useful.