I am not sure you can make the allison transmission with 3 computers talk to the cummins?
if you can figure it out, or know someone who has, or can, then go for it. Otherwise stick to a stock engine trans assembly.
What size truck (the old one) do you have? I would not do the swap with less than a 1 ton, although a 3/4 ton would probably be fine with some people. I don't know how you plan to "strengthen the frame" but I figure that the guys from the factory have done a better job engeneering a heavy frame from the start then you or I can do with a welder and a 1/2 ton frame. That's why I would start with 1 ton plus. By starting with a bigger truck you also get beefy enough axles and brakes to support the swap. Spring leaves can be added to the front to carry the extra weight.
I am currently doing a Detroit Diesel 4-53T conversion in a 48 chevy 2 ton. check the big bolts for the thread.
Grigg