The spacing should be 0.32 on the autolite platinum sparkplugs
One can purchase an Autolite spark plug from a local store that carries Autolite products. One can use the store locator on the official Autolite website to find a location near him or her.
The Packaging. Autolite MAKES Motorcraft
David Underhay The decal on my 1968 3hp Johnson says use either of: Champion J4J, AC M42K, Autolite A21X sparkplugs. You may have to find the current equivalents
Ford sold Autolite to Honeywell when they began manufacuring the Motocraft brand.
It is 605
64 Autolite Replaces Champion RN11YC, NGK BPR5ES
All multiples of 605 are divisible by 605:605, 1210, 1815, 2420, 3025, ...The numbers that 605 is divisible by, ie the numbers that divide 605 exactly, are its factors which are: 1, 5, 11, 55, 121, 605
Sparkplugs are almost universal, because of the way sparkplugs work and the way they are shaped the same, it means you should be able to use "standard" sparkplugs.
605
4 cylinder 2.4 engine, Autolite APP3924 Double Platinum. 6 cylinder 3.0 engine, Autolite APP64 Double Platinum. 6 cylinder 3.3 engine, Autolite APP646 Double Platinum. 6 cylinder 3.8 engine, Autolite APP646 Double Platinum.
The factors of 605 are: 1 5 11 55 121 605