A Ford powered by a Chevy? Subscribed! Has it been done before? Probably! This is your work truck, right? So it doesn't have to be pretty and you guys (the State) don't even check for emissions, right?
Some custom engine to frame mounts, custom transmission crossmember mount, and custom driveshaft at the minimum. Are you planning on a Carb or TBI? Or a Vortec? The only issue I see is the gauges. Truck is going to be down for some time while you sort things out...
Is your tranny going out too? Why not a Triton 5.4 Swap? I think those should be pretty easy to source and they are pretty reliable. I forget the whole 2V vs 3V, and they still have the spark plug issue?
Otherwise probably better to sell the Ford and get a Chevy. Can the utility box be swapped? Or is it specific to the Ford? I used to see a lot of GMT400 C3500 and C3500HDs with those utility beds around here for around $2500-$4000, either from AT&T or the railroad companies. I seem to recall they had low miles for the year and engine and interior always looked better than any comparable "regular" 3/4 or 1 ton.