I just got one of those older ones in a trade, 58 cal. Didn't inspect it much, just noticed the huge firing pin. I thought I would use the receiver on my Versa barrel, and just file down the end of the pin. The frames are noticeably different and incompatible with modern SB1 or 2. This one has an exposed cap nipple for a #11 cap, and requires a wierd wrench to remove the plug...I'll have to fabricate one of those I guess.
Ben