Unless it is a conversion/ speed shifter for a 3-speed the floor shift is an SM-420 4-speed HD truck trans. They also came with 2 versions of 3-speed column shift and an automatic. I don't remember now if the 2-speed Powerglide was still used in 66 or if they were all 3-sped THM 350's. Good luck with it. My 1st pickup was a 66 C10 longbed fleetside with 250-6 and 3-speed. Wish I stll had it! wink


Professional Novice