Gm used to to an endurance test on manual transmissions that they were using in their cars called the "Bonzai Test". EVERY manual transmission tested broke in LARGE pieces except 1 transmission...a Dearborn 3 speed!
Yep! The heavy duty 3-speed was a top-loader ford 3-speed(but it has GM pilot bearing and clutch and throw-out bearing and was installed by Pontiac) I have one that came out of my '65 GTO. I've torn up a couple of 4-speeds and then put the original 3-speed back in and never had a problem with it. Put yours back in it a good tranny!!!!!!!!!!