Thanks Jim. This one is 1-7/8" No part number.
Well, surprise, surprise. A 1 7/8 inch space appears to have a part number of C6OZ-8546-D, Motorcraft YA-81, which was used in 1967 on a 200CID I-6, and starting in Jan, 1966 on a Fairlane with a 390CID engine, W/WO smog. Other applications include Mustangs with a 428CJ (and super), plus a few others. My Ford Car Parts doesn't cover Mercury.
Jim