This could get a bit long---------but-----------74 A-body 8 1/4 shur-grip built by RRP with 3.73:1 gearing. Rebuilt stock leaf suspension. I had an A-999 transmission built for it with Trans-go 2 shift kit and lockup converter. (I didn't want to give up converter slip) I built the car to road trip at 70 MPH at a reasonable RPM. With lockup, 275-60-15 tires and the GV engaged I computer simulated my little 273 would be turning 2400 RPM @ 70 MPH, acceptable to me. I had custom 15" rally wheels built with as much backspace as possible, Cad mockup indicated they would work with no modifications. I had to lower the transmission crossmember about 1.25" and the longer GV tailshaft accentuated the degrees of drop from stock. My first setup I set the pinion angle with an $8 angle finder. On the hunt for the unwanted vibration I bought a digital angle finder and rechecked all my original work. By the GV owners manual checks revealed that the driveline was 3/4" short. I had a new DL built the correct length and installed a positive degree pinion shim of 1.5 degrees. I reassembled all and installed new fluid in the GV. The car runs 2400 RPM @ 70 MPH as calculated. The corrections made to my geometry fixed the vibration issue which never was that bad to begin. We all know harmonic vibration never gets better-only worse. It was a brutal week for this old man but now I can take it to the Olympic Peninsula with confidence.