I've run the 2 inch primary coated and thermal barrier with 3 1/2 collectors on a 74 Swinger. No issues. Fit very well. We have 1 3/4 with 3 inch collectors on the 73 Scamp now too. Have run that a lot on the street. No issues low hanging or bottoming out. Manual steering only with the big primaries. Pretty sure no stock power steering box on the 1 3/4 also. A Borgeson box may cure that. I've not researched the shorty stuff. Do they claim room for stock box and things?