If you take that CW Moss link again, you'll see the third option "....halogen reflector kit" offers both ways; just head light or head light with signal. These are pretty much direct replacements for your existing reflectors and come with retainer clips and three prong pigtails if they're like the ones I put in the coupe. For the signal function they have a hole drilled in the reflector (toward the bottom if I remember correctly) that will hold a second socket with amber bulb, don't think they're LED though.

I don't have a ready reference to link, but someone also makes a turn signal add on kit that consists of a bracket that mounts under the H4 bulb base that has a socket and wiring that enables you to add signals to the basic halogen setup. I suspect most hot rod part suppliers would have access to that kit too.