[BarryGMC]

The floor on a 66 is different than the earlier trucks. its like the 67-72. the auto and 3 speed rigs have a solid floor. the 4x4 and 4 speed trucks have a bolted in high hump. You have to cut out the floor and some of the firewall and graft in the corresponding high hump parts. Also any 420 trans from 47-67 will work. however there are 4 yoke sizes used 1310-1330-1350-1430. There are 2 case styles that were made. The best ones are the 65-67 with the extra ribs cast in the case. Finally nearly all 47-67 gm trucks with a 4 speed have the 420 trans. There is the odd new process 435 in the 60's.