4 speed to 4 speed od clutch chatter

You wouldna liked that od box anyway; the splits are outrageous for a hi-winder. It is a good box for a low-rpm,hi-torque engine. Something like a slanty or a stock teener. Or even a 2bbl 360. But if you got a revver, not so much.
That 3.09low likes 3.23s. or maybe 3.55s. 3.23s will get you 52mph @6400. And at the shift, the Rs will drop to 3460. Your engine got power there? Not much.The 1-2 powerband requirement thus is 6400 less 3460=2941!
Using the 2.66 box by comparison, the Rpm drop from 6400 is to 4595. The powerband requirement is thus 6400 less 4595= 1805; see what I mean?
2941/1805 = plus 63% more powerband requirement.
I tried that tranny. I even blew two of 'em up,before I threw in the towel.
I tell you what tho, if you put a GVOD behind one,and start splitting gears, you get 7 useable gears including double overdrive.