I was taught years ago to set ignition timing and tune the carburetor in gear with an auto trans, even with a stock engine.
My typical RPM drop ranges from 75 -100. I've had some at only 50 RPM drop.
Click key start and ready to romp.
You had better teachers than me!
I found out later. Pretty much right there on the emissions and tune up stickers on the later cars.
I don't always do it in gear, but I'll always check it in gear. Depends on if I have a wall to put the bumper against.