I have a good clutch shaft in my parts bin that does not have the groove at the end for the locating bolt but otherwise is identical to the shaft in my TR6 trans. Moss lists the shafts for 4A and 6 as the same part #. Is the shaft I have without the groove the later shaft. Moss has the early shaft and locating bolt as N/A so maybe it's not necessary to have the grooved shaft and I can use the one I found. maybe it was determined that the locating bolt wasn't necessary?