Mystery back plates

Question for the List:  I've come across a set of rear brake back plates, 
the type using the dual action wheel cylinders, presumably out of a 
Spridget.  One of the plates is marked 4561-132LH, the other is unmarked.  
Can anyone tell me if in fact these plates are from a Spridget and what 
years they were used?
Thanks all.
Ken Stepleton
'58 Bugeye
_________________________________________________________________