I need three speed wiper advice/help

i have a 1970 Coronet that I’m converting from two speed to three speed windshield wipers. I live in the arctic, I can’t just go down the block and buy a three speed motor. The one I have is junk. To help my search I need to know if the motor/gear assemblies from other years and body styles will work. I’m aware that there are rebuilders. That’s not my question. I would actually need a core to rebuild.

Yes, they're interchangeable but you want one from a '69 or later car. Unless you're doing a 100 point resto, you can rebuild these yourself - they're straight forward and the factory service manual has some info. If you do want a restored unit, SMS Auto (Stefan Fournier) is in Canada and is one of the best. Given your location and the cost of a core you might be further ahead to buy one without supplying a core.

Or....you can find one from a C-body (common) & grind the opposite side of the your linkage arm with a rat tail file to round it off & the c-body one will bolt up/work. My car has had a c-body wiper motor for 30 yrs.