I see nothing wrong with your direction. But, it would be helpful to know which year C4 the IRS suspension came out of.
The length of the camber rod will effectively change the exponent in the camber gain... and it will also have an effect on bumpsteer... but for the worse, not the better. The reality of this is... that with the limited suspension travel you are dealing with... this effect will be infinitesmal.
The reason to know the year of the IRS is that GM made a toe system change to the 88 and later suspension to correct for a toe issue of the previous years. The use of the 88 system would help to reduce, or maybe even negate, the creation any other issues related to the effects of bumpsteer when shortening the camber rods.
It looks like a cool little project !
