No, it's not nearly that bad. You don't actually need to drop the steering column. Somewhere I have buried a photo of my old 124 wagon looking very much the same.

Seriously, the heater core is inside the same box as the a/c evaporator. It's essentially the same job to replace either one. So all the discussions around evap replacement in a 124 also apply to heater core replacement. Given the labor you want to make darn sure the heater core is the problem before tackling the job.

On the other hand, ethelyne glycol (AKA anti-freeze) is quite poisonous, and delivering it as a vapor is the most effective way to deliver it to your body. I personally wouldn't ride in a car with a leaking heater core.

- JimY