Jack,
This cat can be skinned many ways. I much prefer the momentary contact switch plus relay method to the toggle because it automatically disconnects the OD when you shift out of forth. With the long shifter stick, putting a switch on the shifter gets very complicated. With a remote shifter it is a little less so, but still pretty tricky. The ipd switch mounted on the turnsignal switch housing is a possibility I haven't tried because I didn't trust its sturdiness. Your turnsignal switch already incorporating the headlight dimmer, I would say that mounting a momentary contact switch and a light on the dash would probably be the simplest approach. If you don't want to make more holes in the dash, you could mount them on a bracket below the dash in the vicinity of the shifter. Anyway, substitute the numbers 689044, 870849, and 695288 for the one in the BB address on the top of this page and you'll find more useful info on this subject.
Bob S.