"I am new to this site and have some q's about 4spd options for the 1967 ss 350. My car is all number matching with protect-o-plate. The Rear end code that matches the protect-o-plate is PL0919G
Daniel is correct. PL is only used to identify the axle type. In your case a 3.55:1, 12 bolt, Non Posi. Built Sept. 19, 1st Shift".
"I thought the close ratio Muncies where installed in z's and big blocks"?
That's correct. The M21 was for Z28's, L34's & L78's.
Can you post pics of the POP, the cowl, the Vin #, and the engine pad? If you have trouble posting pics send them to my email address & I'll try to post them for you.