I think Dodge trucks used the front motor mount and the 2 on the side at the bell into the early 60s. Usually you ended up cutting the two side brackets off the original frame if you went with a modern motor mounting system.

I installed a small block Mopar in a 54 Dodge pickup, on that one I used an F,M, & J (Aspen/Volari) clip. Even with that, the small block protruded into the cab the full width of the motor & exhaust manifolds and was 6" deep. The "new" firewall was about even with the bottom of the dash. The motor sat low enough there was plenty of clearance to the hood. Unless your truck body is deeply channeled over the frame, I think you will have enough clearance for an air cleaner assembly. The air cleaner assembly should sit forward of the dash. There still should be enough clearance for the fresh air vent on the cowl as well, but you may need to do some careful firewall notch design.

I did a 50 Dodge truck, and that motor also protruded into the cab, and my 39 on the Dakota frame also protrudes into the cab. I think its because Dodge set the original motors in the original trucks centered above the front axle, and the modern motors are longer then the original flathead 6s were and are designed to sit farther back. My 54 was an original V8 truck, so who knows. It was lacking its original motor when I got the truck. Gene