4 speed to 4 speed od clutch chatter

Only fork I have is the one from an o/d 4 speed car. I used it for 5 years with a normal 833 bellhousing with small retainer with plain 833

So I did have an o/d fork, od bellhousing with correct pivot with the od trans.

What gets me is I kept the OD bellhousing on the car today, the same fork/throw out bearing I used with both transmission. The same free play for the clutch and It does not chatter with my original 4 speed. I used a 3 speed retainer on my original 4 speed(small bolt pattern with the 5in plus diameter) so I could make sure bellhousing wasn't causing issues.

If it works perfect right now with a standard 4 speed, od bell, fork I have along with the other parts then I should be able to un bolt trans,swap just the box and should be the same. Not the case