Headlight/alt. Wiring harness question

[Dads 68 GMC]

I am installing the original h/l wiring harnessfrom the 68 gmc. this h/l wiring harness does not have wires for the side marker ( the 68 just had a blank) can I splice into my front park/signal wires or should I try to get a harness that already has them(69-72) I think?
My other question, I installed a new alternater ACDelco p/n 19151858 with a built in voltage regulater that just needs a hot wire to ignite it, how do I wire it? the hot wire to the old alt.? & do I use any of the wires from the old voltage regulater? any help is appreciated.