The replacement transmission and bellhousing are from a 55 first and or second series truck with a 235 engine. 55 V8 trucks and all later trucks used the configuration as in your first photo. Simply remove the side covers and swap them over. Be aware that the 2-3 shift forks are a common wear item. You can use the shift fork from the replacement if it is better or get a new one.
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