Just some general questions: What is the 9.5" converter's stall rating? If this is a race car, then why on 3.91? 3.91 with a 28" tire is like a 3.55 with a 26" tall tire.
If you plan to run the cam with the 3.91s and the 28" tall tires, then I would advance the cam 4 degrees, IF you have enough piston to valve clearance.
If it was me I would swap the converter and transmission first to see where you are. The converter and trans swap may improve your MPH at the finish line and affect rear gear selection.
The longer cam duration won't affect max torque, just move it up in the power band. With only 8 degrees additional duration the power should migrate roughly 400 RPM higher. Make sure your valve springs are up to the additional RPM shift points. The tighter lobe separation angle should help it build more peak HP and torque.
The real trick is will the new converter stall let you take advantage of the additional torque higher in the curve.