One of the street rods I've seen recently had spacers made to set the manifolds out away from the motor, then they ran the exhaust outside of the frame. Wasn't a big block, but it was Mopar and on a Dakota frame. Think the spacers set the manifolds about 2" - 2 1/2" out, simple machined tubes that had bolts go through the manifold, the spacers, and into the heads, two sets of gaskets.

Also wondering if you use a short tilt steering column, can you run the bottom closer to the floor pan and run the column under the exhaust? Stands the column more up right, but the with the tilt and a longer column mount at the dash can make a lot more room under the hood, you just need the steering wheel to end up in the correct position to drive it comfortably. Gene