I have a 518 behind my 540 Hemi with 3.91s. I love it and am glad I went to all the effort to put it in my Cuda. And that experience causes me to ask some questions about putting a 518 behind a 440 to do that particular job.

First, someone check my math here, but isn't the final drive ratio of 3.23s with the .69 OD of the 518 something like 2.23? And I get that a 440/518/3.23 would RPM about 1,900 @ 70mph. If that's ballpark, I think there are some additional things to consider.

Is the 5,300 lb loaded or empty weight? Are you going to use a lock-up 518? If not, are you concerned that the RPM at hiway speed may allow a lot of converter slip with that much weight and pushing a lot of air? Would there be a concern that the 440's RPM would be low enough at hiway speed that it wouldn't have enough torque to pull the weight and push the air without eating a bunch of gas?

I am not saying that this combo won't work. I am only asking if it would be as efficient as the OP wants.