Dennis,
The Fox .15 first appeared in about 1958 as the "steel fin" version. It came in a brownish colored box and I THINK it had the "X" designation. Sometime later they switched to the "slant plug" version with the drop-in liner. Don't remember the year. Perhaps that is the version you are thinking of. All of my Fox .15's are in CL version up to the schneurle when I have them in CL and RC (both bushing and BB).
I saw a baffle Fox .15RC on the bay in the last couple of days.

George