ChuckLee,
You are doing a great job and your truck is bad ass, we are all learning as we go and even if you have done a bunch of these trucks you should learn something new with each one.
As for the rods go with the forged ones, RPMs are cool
As for gearing here is what I came up with.
275/40/20 tire= 28.66" tall.
F-Body T56 if stock has a .50 first gear.
4.11 gear at 75 MPH= 1807 engine RPM and 3614 DS RPM.
4.56 gear at 75 RPM= 2005 engine RPM and 4010 DS RPM
4.88 gear at 75 RPM= 2145 engine RPM and 4290 DS RPM
With that I would prefer the 4.88s with you having a motor built to make power in the upper RPMs. The issue is drive shaft speed of 4290 is spinning it pretty fast, if a long bed you will need a two piece for sure and even at that it will need to be built right, if a short bed you can try a one piece as I am. My set up puts my drive shaft at 3830 RPM at 75 MPH and I went with a 4"x.085 wall steel driveshaft.