360 into 64

Where did you get that info? Much of it is wrong. There were no externally balanced 318's or slant 6's. The first 904 behind a 360 was in '75 and it wasn't a 999. The later speed gear were just a different design. The opening in the extension housing remained the same. They just eliminated the adapter and mounted the gear on the speedo cable housing. You can tow an automatic for short distances at slow speeds and not do any damage. There are other gaffs, but I'm tired of typing......