440 max wedge

Yup. What you need to do is determine WHAT you have for cylinder heads. Some of the motor home heads take 18mm Ford type plugs. "I guess" some of the aftermarket heads take "peanut" 14mm "tapered seat" plugs.

And there is/ was no such thing as a "440 max wedge." If you happen to have legitimate 413/ 426 maxie heads ( I doubt it) they take "standard" B/RB plugs, IE 14mm gasketed