Frankly swapping chassis' over a heater core is a little absurd unless the car is a total POS to begin with.

I've done multiple heater cores and evaporators, and its not hard. The 124 one bills at like 20 hours or something. My first go was around 7.5 hours in and out.

You're a proficient technician, just replace the heater core. Its not that big of a deal. I gather you've parted out lots of cars, if you've ever pulled a parts car dash you're already way ahead of the curve in terms of getting it apart efficiently.

My best advice is if you're doing it inside (I.e. Not out in the rain) open the sunroof. The extra light goes a long way. On a 124 I don't pull the seats as some suggest, just slide them all the way back.

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