The purpose of side marker lights is to indicate the presence of the vehicle as viewed from the side. Thus, they would need to be near the front and near the rear, with both being high enough to be noticed. That somewhat limits where you can put them on your Advance Design truck. You have stated that you don't care for the period aftermarket turnsignals, although I think that would look fine and you could stick one of those small halogen or LED lights out the side of the housing. Another alternative for the front would be to see if one could drill a hole in the side of the headlight ring and fit a small light there. Reproduction rings are available and you wouldn't be cutting a hole in the fender.
At the rear, some people like to put lights in the circular bed rail hole at the rear. Perhaps you could modify one to stick out the back and point sideways. That would also be a modification that could be reversed, if desired.
For a daily...I mean nightly driver, I think your idea has merit.
Kent
