As HRL stated 4 bolt side cover units are Muncie's even though some of them were made in the Saganaw plant.
The transmission you have is likely from a Nova or Chevelle with the correct truck side cover. A 64-66 truck would
have had a short tail housing. (except for overdrive units). GM changed the gear "pitch" in 64 and none of the
internal components interchange with the 63 and earlier units. It may be a bit more "heavy duty" than the earlier
transmissions as some of the gears are slightly wider.
Fred


1956 3100 Pickup/Red/350/3sp OD/PS/Disc Brakes
1957 Bel Air Sport Coupe/Red/355/TH350/PS/Disc Brakes
2017 Silverado LT Single Cab SB/Black/5.3/6 Speed Trans
1947 Willys CJ2A w/F-Head engine