440 motor mounts

The 66 New Yorker and 71 Imperial use the same 440 mount brackets as the 66-72 B body and the 70-74 E body. Many many years ago before conversion mounts were available with instructions for $159/pair, we used to do what you propose: Cut the mount ears off of a B or E body K frame (the ears are the same on small block or big block) bolt them to the motor, drop in the motor and transmission, tie down the trans mount, then tack in the ears, pull the entire thing back out and finish the welds. It would drop in like it was made to be there.

I even had a bare big (short) block fabbed up with an empty transmission case bolted to it as a lightweight jig, so the job would be easier. We also did the spool mount K frames the same way, cut off the posts and tacked them back in with the tranny in place.

You are also correct about the motor plate. If the tranny is in right, you can tack in the motor plate mount brackets as well

What I remember most about doing it that way was that it was a HELL of a lot of work! Back then it was the only way to do the job, but is it worth all of that to save $175?

The Schumacher mounts still require a small notch on the K frame for oil pump clearance, but other than that it's a 1-2 hour job setting that motor in place with conversion mounts. Here's a link to the instructions:
http://engine-swaps.com/Pages/InstructionPages/A67BRB.html

BTW, if you have a v8 K frame in your 72, I have a set of the Schumacher mounts (small V-8 to RB V-8 ) that you can have for $50 plus the 440 mount brackets from the Imperial or the New Yorker. If you have TWO sets of 440 mount brackets, I'll trade you even.