It is amazing what discoveries are made during the cleaning process.  The tip of the screwdriver blade, circled in red, is pointing at a minute stamped number.  Each of the 4 sub-frame mounting lugs is numbered: -

1 = left hand front

2 = left hand rear

3 = right hand rear

4 = right hand front

Numbers 1 & 2 are stamped the correct way; 3 & 4 are inverted. 

An inverted number 3.

As with all other parts on this engine, the bridge pieces and shims are stamped with the casting identifier V26.  These two pieces belong to the left hand rear clamp.

A complete set.  Note that the studs are of unequal length and that the seating washers into the bridge are radiused.

The two remade shims, one each of 3 & 4, will be filed down to the correct thickness during assembly.