Jeez Ron, why didn't you ask me about that axle? Its a Chrysler corporate 8.75 full floater, if I remember correctly. I have another one under a dually 58 parts truck. They are kind of an odd bird. They came with 4.1:1 or 4.89:1 gears.
The 9.65 you referenced is used in flat fender Power Wagons and military trucks only (3/4 ton WC's and M37's, the earlier 1/2 ton WC's are a little bit different). And only ever came with 4.89:1 or 5.89:1 gears.
You should be ok bolting an LA engine to the NP420, but you will probably need a different bellhousing. The bellhousing in the truck is the same bolt pattern as an LA, and will bolt up, but the indexing of the crank flange and flywheel will be different, so your clutch won't work. The 315 poly you have is the tall deck Dodge hemi block, and while that flywheel and bellhousing will fit any early hemi engine (because for some reason those are the only things they all have in common) the A and LA stuff is just different enough to be a pain. A 60's era hydraulic truck bellhousing is probably the ticket, at that time they were still using the NP420, as well as the NP435 and the NP540 and shared a common bellhousing throughout. Some of them even fit small block, big block, and slant 6.
The 9.65 you referenced is used in flat fender Power Wagons and military trucks only (3/4 ton WC's and M37's, the earlier 1/2 ton WC's are a little bit different). And only ever came with 4.89:1 or 5.89:1 gears.
You should be ok bolting an LA engine to the NP420, but you will probably need a different bellhousing. The bellhousing in the truck is the same bolt pattern as an LA, and will bolt up, but the indexing of the crank flange and flywheel will be different, so your clutch won't work. The 315 poly you have is the tall deck Dodge hemi block, and while that flywheel and bellhousing will fit any early hemi engine (because for some reason those are the only things they all have in common) the A and LA stuff is just different enough to be a pain. A 60's era hydraulic truck bellhousing is probably the ticket, at that time they were still using the NP420, as well as the NP435 and the NP540 and shared a common bellhousing throughout. Some of them even fit small block, big block, and slant 6.