I have very little knowledge in "building" a 6 cylinder, but will say that a stock 6-292 is a real good engine. In a truck, I actually prefer a 292 over a small block V-8. I had a 292 in a '64 C-30 and it had plenty of power. It was all stock, except for the exhaust and a slightly shaved head as they found the head a little warped when I sent it out for a valve job. Fully loaded at 10,000 plus pounds was no problem going uphill. You will have more gears to pick from than I did, which will make it even better.
For the exhaust, I used a GMC V-6 straight thru muffler. Letting these engines breathe better will add to the power.
