so if I want to put a 518 in my 70 Cuda with a smallblock, what donor vehicle should I look for? What is the OD ratio? Will I need to make any modifications to the floorpan or crossmember, or just a shorter driveshaft?

67 Dart GT 340 4 speed
70 AAR Cuda 408 6 barrel
96 Indy Ram original owner
2011 Hemi Durango