It should be the exact same part. I think you'll find that 4" is the total length and 3 7/16" should be the distance between the two holes for the screws.
Newmar, I believe, used Autotex components during that time with their pantographic wipers.
There's two plates available ...one that is used for a "wet wiper" arm and one without. Yours appears to have the "washer" so you'd need the part 200242 (
200241 is the same without the washer kit).
AutoTex 200242 - Pantograph adapter for Wet (washer kit installed) Wiper Arms - $15.99