Lee Six was Chet Brown's partner when they started out. They split around 1976 or so and Lee formed his own company. I liked Lee Six sporter stocks better than Brown Precision only because the molding was better which made fitting and finishing easier. The Six stocks were a bit heavier because they used more resin. Sporter styles were a bit thicker in the grip.
BR stocks from the two companies were similar in design and construction though they diverged a bit as time went by.
I think it was around 1984 that Lee Six started making the IM stocks which, just like similar offerings today, were really just cheap crap.
Lee was a very nice fellow to deal with and a fun competitor at BR matches. GD