Hello, Amir..I reckon that this query to the List must relate to the pin-striping on your "randonneuse" - jpgs of which you sent me this morning.
If that is the case I am sorry to have to disappoint you, as the frame in those jpgs isn't an Alcyon...but it is a super enough frame. Alcyons..I have several of them, usually have fairly simple double-box lining, or at least mine have. All my Alcyons of the vintage that your frame is, are bronze-welded, not lugged.
Your frame is a real puzzzler, because it has a very 1930/40s rear triangle, with those vertical drop-outs, brake studs brazed under the chainstays, b/o chainstay protector etc etc..and the Crozet cast bracket. The front end is more 1950s and appears to have Oscar Egg pressed head lugs and a similar period fork crown. It could be that the lugs are cast..but I cannot make that out from the photos. If they are cast then they could well be one of Crozet's patterns.
The frame is very similar to an un-named one that I have, which I have been told is probably an Oscar Egg "Grand Sport" or "Super Sport" both of which were 650 Randonneurs. Trouble for me is that the fork is not original..and I would expect the original one to have an engraved or stamped crown with "Oscar EGG".
Your frame remind me very much of a RIVA-SPORT which I think should be joining my collection soon..so I will keep you posted.
Norris Lockley..from a very wet Settle UK