It'll bolt up, but the travel isn't ideal... The stock 70 Chevelle box has 40 1/2 degrees of travel; the IROC will have somewhere around 32-35 depending on which box and year it is. It looks to me that the Jeep Grand Cherokee is the box to have - 12.7:1 ratio and 43 3/4 degrees of travel.



Check out this spreadsheet on the Chevelles.com page that shows ratio, effort, and travel for all manner of boxes.

http://www.chevelles.com/techref/shea_3.html