I don't have my books in front of my right now but it looks to me like it could be an O-108, but I'll do some more checking on my lunch break, because I'm not quite sure.
Ok I did some checking and it looks to me to be an O-108a which is an R3 coin. There should be some die lines between the end of the bust and the edge, which I think I can see in the second photo of the obverse, the five should be slightly higher than the 0 and tipped to the left and the C in 50 C is sharply tipped to the left, additionally A3 on the right leg is broadened from a die chip. If anyone thinks I've got the wrong one just let me know.
hey robec if you want to PM me the address for the next person on the list for that Proof lincoln. :high5: