Pretty sure the narrow washer, o ring and support washer all are stacked downstream of the layshaft support bearing and the order listed is upstream to downstream
In other words looking from the clutch end rearwards towards the endcase it's narrow washer, O ring, Support (thick) washer. After that its the speedo worm/seal runner
A long time back I made a wee write up on the 5 speed box, when I stripped a LM 1000, if its any help, but as you've been there before its probably not required
John