Rear axle assembly - reccomendation?

This is great info...it's a matter of offset, right?

Any leads on where to learn about A-Body Duster/Demon/Sport wheel wells and what offsets might best accomplish this?

Yes, the offset is key. More information is available in a thread here @ FABO.

I appreciate that but I've consistently been steered away from 8.25" due to the C-clips, availability of components, etc...also, they're not as stout as an 8.75, no? I'm thinking that slicks might spell the end of one of those.

The 8-1/4 gets a bad rap due to the size and C-clips. While C-clips can fail, it is when there under abuse there limitations arise. If the car is going to spend a lot of time with slicks and at the track, something larger may be a good move. Normal and occasional spirited driving is fine.
I have not noticed a shortage of components or selection of ratios. These rear can hold 400HP all day long. While the 8-3/4 is a much more stout part, the price is reflected.

No matter what rear you use, there is something some one could point at as a short coming.
What is the intended power level?