Do you have something worked out as a source for the stripper clips?
Also, you should consider mounting the front end of the SMG-60 on a 68 Special body. The back of the SMG-60 that holds the back cap is thinner than on the 68 Special and more likely to crack.
I currently have a SMG-60/68 Special hybrid that Runningriot converted to 68 cal. My only issue is finding 68 cal stripper clips.