He would have been Elvis if Elvis wasn't Elvis. ;-)Conway had a leather wrapped '57 Roundup, which is an oddity in and of itself, since the model was seemingly discontinued circa 1955. But there was a batch made in '57. Maybe Ed can shed some more light on that.
I can't find a picture, but what's even odder is that the other guitar player in his band at the time had what appears to be a late '57 or early '58 Roundup with FilterTrons and a mud switch, which is something that shouldn't exist at all. My guess is that maybe at the very tail end of that '57 batch they made the switch to FilterTrons.