64 3 sp to 77 4/OD Installation

76 feather duster. I had one that came with an auto but generally were 833 OD yes alum case does help weight,too, as the feather duster had some aluminum parts to help weight. the super six of that time was a 225 with 2 bbl
I understand A/JFormS comment bout the OD as related to power of the a 170 slant, which my 62 lancer has but I also have a 833 and a 3 speed out of 72 duster I can use, the 3 on tree does not remind me of my childhood so it will GO away.