1. All the COE's I've seen with V8's have the engine behind the cab. But I think all the v8 COE are on modern frames and sit lower on the chassis. I will not put the engine behind the cab.
You've answered part of the problem right there. Modern frames and hugging the ground leave little room for the engine.
A guy I know up the road from me has an early 50's COE and he's running a 292 with a downdraft carb. He may have jacked it up a little, but the thing is running larger tires anyways and it sits very tall.
If he can squeeze a 292 with downdraft in, you should be able to fit a 348.
Jeff