I'm going to jump in and give my $.02. Having built quite a few TBI engines in trucks and researching camshafts I have come to the following conclusions:
computer controlled engines like min 112 lobe center camshafts. this gives the map a better signal, higher vacuum
400 SB like 106 intake lobe center line.
with a vehicle this heavy, and with a flat tappet camshaft(not roller) my recommendation would be a 209/216 @.050 lift. this cam is available through Elgin Industries. I have personally used this cam in a 4 wd drive truck application towing a boat through the mountains of AZ. This engine was a 383.
As for intake manifold's the edelbrock 3705 is eddy's version of a tbi manifold, it only has a 11% drop in flow from an open head on a flow bench. I tested this, the stock manifold as someone said is junk, it has a 20% drop in flow on the same head.
As for your going to a 700R4, Don't do it with that heavy of vehicle unless you like R-R ing transmissions and buying parts. The tranny wasn't made to do that much weight. Stick with your 400. 3.5 tons is a lot of weight to get moving.
When you get this all done, don't forget to change the injectors to the police car style injector, the stock 350's just can't supply the fuel with the modifications you made.
You didn't say what size tire you have on this vehicle. This will affect the final drive ratio.
I hope this gives you some direction on your project. Yes Isky makes great camshafts, and a comp 268 works well up to about 4800 rpm, however it is short on power, depending on what cyl head you have on the engine.

Good luck