I like that you took time to add flow bench numbers. As anyone who works with these engines knows the cylinder heads are the biggest limitation to making power. These engines where designed for low speed torque, basically as is often said here "A Tractor Engine". Jerry is right with his observations but there are those of us who just want to push the issue a little farther.
I have worked with a 292 head, modified with use of lump ports and some combustion chamber work along with port matching. I don't have access to a flow bench so there are no numbers to back anything up. The end result was a very strong running 292 (bored to 301) with a great lope to the idle and responsive throttle. You will need to do your homework. There are several sources for information, the book I keep returning to is "Chevrolet Inline Six-Cylinder Power Manual, 2nd Edition by Leo Santucci". There is a tone of information and refences in this book.
If you just want to watch something on building a Hot Rod Six, Stacy David did a segment on Gears, just worth watching.
In the end it comes down to "It's your Truck, do what you want". I'll be following along.
