Nova,
Hopefully I can shed some light on this.
With that size tire & wheel, along with the 5" ride height, you'll want to shoot for a tire bulge-to-bulge of 63", not 66.5" like you had mentioned. As you lower the car (especially down to the point you mentioned), you need to suck the tires in quite far. Don't worry, it doesn't look goofy.
With our narrowed C5 suspension, the "hub-to-hub" of 57.5" that was told to you was actually a bit misleading. That measurement includes the stock rotors, so 57.5" is the "wheel mounting width".
So, a wide hub track and a narrow bulge-to-bulge requires lots of backspace. Assuming a 9-7/8" sidewall width, you'll need about 6.38" of backspace on a 8" wide wheel. Shop around to see if you can get the style of wheel you like in that offset.
Another issue that Kevin may have brought up is engine set-back. The C5 suspension is designed to have the engine set far back from spindle C/L, just like a production C5. That feature has been maintained with our suspension due to the positioning of the rack and pinion. However, we are nearly complete with a re-design that places the rack in a much more favorable location that will require little to no engine set-back for small block engines, all while maintaining excellent geometry.
We've done C5 IFS on a Chevy II before, but it's a squeeze. But as you know, it looks great and handles awesome.
Matt Jones
Mechanical Engineer, Art Morrison Ent.
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