Glad you are making progress and the engine sounds great! But I'd like to offer my on your wheel width.

If you want to have as much traction and consistency as possible, I'd suggest getting a wheel that is as wide as possible. Considering the narrow size you are looking at, I'm guessing you don't plan on tubbing it. But I'm pretty sure an E-body wheelwell will accomodate at least a 10" rim with whatever width tire you plan on fitting into it. The widest tire you can fit will work best with a wheel that is at least the same width or even 1"-2" wider! This will provide a flatter footprint while allowing you to run more air pressure for a more stable tire. Wrinkled/wadded-up sidewalls may look impressive, but that "wrinkle" can transfer to the tread surface of the tire and reduce traction. Plus, the higher pressure will help the sidewalls, thus the slicks, last/work longer.
Stock class cars tend to run 9" slicks on 10" rims!