Part of what makes the modern Hemi work so well is the OD trans. Without the OD, the gas mileage will probably not be much better (might be worse) then your current V8. On a truck, your looking at moving the existing trans crossmember back and drilling some holes, and having a driveshaft cut. A factory modern Hemi trans is a stronger trans then a standard 727. It also seems to me that the bolt pattern on the bell was different then a small block pattern, but that could be wrong.

When we did the 5.7 in my son's 57 Dodge wagon, we used a fuel tank and its in tank pump from a mid or late 90s S10 pickup. It will probably fit in the frame behind the rear axle on your truck, the tank is in the rear most foot well (behind the rear axle) of the wagon. We did have to add an adjustable fuel regulator with a return line back to the tank. The S10 tank and pump new cost about 1/3 of anything Dodge related and will do the job, with the addition of regulator and return line. We used the Hot Wire harness.

Its not a cheap swap, but don't cause more issues by trying do it on the cheap. Those corners you cut will come back to haunt you. Gene