Fixer,
You have an interesting rifle. I own Hawken SN 308 that was also built by Ron Paull. The markings on the barrel are positioned the same as yours.
As Buck said, GRRW built a number of left handed rifles, but they were limited by the available components back in the 1970s and had to compromise on some of their customer's requests.
Building a left hand rifle with a right hand lock was often one of those compromises. Yours is the first flintlock I've heard of set up that way, but I know of several percussion arms they built like that. I own a classic "Bridger" pattern Hawken with 1-1/8" barrel set up as a left handed rifle with right hand lock.
Ron Long had designed a left hand percussion lock and a left hand 1" breech plug by the beginning of 1977, but he never produced a left hand breech plug for a 1-1/8" barrel. In this instance, GRRW's only choice to fill the customer's request was to build a left handed rifle with the right hand 1-1/8" breech and right hand lock.
The situation for your rifle was probably similar in that a suitable left hand flintlock may not have been available when your rifle was built.
Speaking of rifles with no cheek-piece, I have a GRRW Leman Indian Rifle that is left handed and has no cheek-piece. Carl Walker says this was the way the customer ordered it.
For a while, GRRW advertised themselves as a "Custom Gun Shop". Throughout their operations, they offered extra options that allowed customers to order customized rifles. These left handed rifles fit in that category of custom guns.
The rifle in my collection with the most custom features is a Leman half stock that is left handed, has the optional lower entry pipe and unique pewter nose cap, extra fancy wood, double set triggers, weeping heart inlays, and a square cheek-piece rather than the beaver tail that GRRW usually put on their half stock Leman rifles.
Did I mention the outstanding wood?
Phil Meek