whoops. i've now found the article at classic lightweights which i had misunderstood to mean that there were two sizes of standard bottom bracket cups. but i now see that the 5/16th" balls were only used with oversized cups. my 1007 axle requires part numbers 1616 1617 and 1618.
there is currently a full NOS set on ebay which i may bid on but if anyone has a NOS or excellent pair of cups and lockring i have a 1954 Gillott road path awaiting.
thanks,
simon bird
london
uk