Is that an issue or difference over 67-up? Either way your cutting the floor board if its not a Silver State kit. I don't trust the machining done by Silver State to have not compromised the strength and seal any leaks.
FYI for all, Hurst kit install.
HURST DRIVELINE CONVERSIONS Mopar 1967-76 A-Body ยป HURST DRIVELINE CONVERSIONS