Old Amana elec furnace

Anyone got a fix on how old Amana furnaces are date coded. Had a very old house today for a 4 point. Everything in it was old and data tags either gone or faded.
Managed to get the S/N - AD65700140
I know Amana was bought out by Goodman (why?) and their new coding is not the same. I have a matrix for most makers but old Amana’s is a mystery. Thanks

There seems to be a lot of disagreement on Amana. Most of the information I have on Amana indicates that they used the BLACKHORSE coding system. So that furnace would be either 1973 or 1983 (that was the problem with BLACKHORSE). I also have a phone number where you can call with the serial number, 416-787-5130. I have not used it in several years.

Thanks!. I have that same information but thought there might be some definative information lurking out there. I came up with the same dates. Your help is greatly appreciated.