Need your wheel suggestions please!!!

OK, after a week of thinking about it, here's where I'm at.

I found a local guy here who will cut and weld the housing, plus cut and re-spline my brand new axles. He owns a race car/fabrication shop and does this for quite a few local racers. He came highly recommended.

My question now becomes, how much do I have the rear end narrowed?

If I shorten it 2 1/2 inches on each side, that would bring my backspace to exactly 5 inches on a 10 inch wheel. Is this right? Doesn't seem like much to me.

The wheel is available with 3.5, 4, 4.5, 5 and 6.5 inch backspacing off the shelf.