Hugh, Viking were making Severn Valley's in 1950 for certain. I have an original catalogue from that year with it listed. The 50 model was 72 parallel with 10.5" bracket height, Fork rake 2.25". Interestingly the brazed on lamp bracket was an extra it actually says in the catalogue (Not fitted unless specified). I always thought that the second two digits in the number where the year. This would make yours 1951 if this statement is proved correct. You need a real expert for the definitive answer. The Campag ends could have been put on later as was the fashion. I had loads of frames converted to modern ends in the mid 60's. Best wishes Joe. Croeso Cymru Joe King Nr. Maenaddwyn Ynys Mon Wales