Ed,
As you well know, I'm as big a stickler as you'll find when it comes to truck originality. BUT, I say, leave 'em on!!! I've always liked the marker lights. They look cool, aid in "visable-ness" (yes, made up a word there! ;-) and by the '60s, I think were a regular item. Nobody will complain about them.
They must have eventually been mandated by code, since the original department added them to my '68 Seagrave. Funny thing - it's an OPEN CAB! They put them on the top of the windshield frame.
My recessionary two-cents worth, anyway!!!
-Michael