366 / 427 help

[Nobighurry]

So I have a 1970 c60 with a 366, 4 speed with 2sp rear. Truck weighs 10800# empty with a gvwr of 24k. I can legally carry around 6.5 tons. Truck only has 34k miles. My problem is it falls flat on hills. I'm in mid-South Carolina, so I'm not talking mountains. Truck runs good, just powerless on hills. I try to avoid full loads just because of the weakness. I can drop from 53 mph to 25 mph on hills. It really isnt safe with that much of a drop.
I have changed it to electronic ignition, new edlebrock 650 carb, plugs,wires etc.
I found a new/remaned 427td but it's going to take $4700 to get it. If I knew the 427 would give me what I need (power wise) I wouldn't have a problem doing it.
I'm hoping someone here has experience with both engines. Any ideas?