A 435 will have an un-synchronized granny gear. A 445 has a synchronized 1 gear that's not as deep. Other than casting numbers the easiest way to tell the difference is the top cover plate, 445 has a bigger cover. 2WD and 4WD are different due to the rear face of the case.
You will need to find a bell housing and inspection cover for a truck not a car. The flywheel is larger, needing more space and I think the Z bar location is different too. Big Block truck bell housings are very very hard to find. Nearly all Mopar bell housings have at least 3 sets of bolt holes for mounting various transmissions. Trans input bearing retainer diameters can be different, but all trucks (that I've ever messed with) are the same. But double check the trans and bell housing anyway. The flywheel MUST be from a 440 not a 400, the balance on a forged crank truck 400 is unique.
One thing that is almost always forgotten with this time of conversion is the floor brace for the inside of the cab. You can put the under floor bracket (with the Z-bar pivot) in with out it but it will eventually destroy the floor pan. The inside half is bigger, make sure you get both sides.
These 4 speeds are also shorter than automatics, that means a different driveshaft. In my experience the only 4 speeds with a one piece shaft have been Regular cab short box trucks. A one-piece drive shaft for your planned configuration is going to be very long (longer than any stock application?) and will be prone to vibration and/or U-joint failures. A two-piece shaft will be the way to go. The rear half is going to be the same on basically anything with a two-piece shaft based on rear axle. The front half is where the difference is found, this may have to be custom made if you can't find the exact right used piece. Check U-joint size possible difference from the axle to the drive shafts, you may need a conversion joint (2 different sizes) .
And your floor pan needs to be changed! As a early 2WD automatic the floor pan the lowest version ever used and the center hump is not a bolt in style. That trans will be higher than your current floor pan. You can cut it out and add a higher bolt in style, weld in or bolt in is fine. Room to work is very limited under the dash. You WILL need to find and early (72-74) 4 speed or 4WD hump. The floor pan changed in 1975 and those newer humps will not fit the back 8 inches near the seat.
The starter relay will need to be changed or a jumper added to bypass the neutral safety switch. Speedometer cable should be the same. Trans mount cross member will be the same, the mount will have to be reversed. And there probably another dozen things that need to be considered but they are minor things.
Good luck (finding parts first)!
