Winchester Mod. 63 X
I know this is a long shot but I just purchased a groove-top Win. 63, serial number 163587x. Winchester added the x to serial numbers that were duplicated. The chances of ever finding that other gun with the same number is pretty remote but I thought stranger things have happened. The condition is nearly unfired condition. I would love to put those two guns together. Perhaps the owner of that missing link will read this post. There were only 10,000 grooved 63's so the chance may be a shade better than remote.