Ah! OK. The scroll that you had was modified for use only in a Sears early 12" machine. For some reason, Sears insisted on having the mechanical interlock that prevented the operator from engaging both drives at the same time. None of the Atlas machines had this feature, which I consider to be unnecessary. And it was not on the late 1/2" bed 12" machines made 1957 - 1981. Neither were the other oddities. The machined flat was dropped after 1957. And the replacement scrolls became the same for 10" and 12" machines.
I wouldn't say that it is worth disassembling the apron to remove them but you could have simply omitted the interlock parts (Plunger, Spring and Spacer) and used the scroll as received. Sorry that I didn't think of that.