Roughly about 14-15 years ago there was a member on Jolly's site that completely restored a White 68 GMC K2500 series with a 305E. His name was Jake and advertised himself as Jakes General Store, well Jake converted his truck from a 4 speed manual to a 700R4 automatic overdrive. As it's been discussed before is "Bendtsens" makes the adapter for the GMC V6,
www.transmissionadapters.com.