Ju87-R1 armor?

Two very heavy iron fragments from the crash site of the Ju87-R1, Scandinavia, each weighing approximately 20 kg, measuring 50 cm by 25 cm, with a thickness of 20 mm.
One of them has a raised number—R8-87.955-0701.
The parts list for the Ju87-B1 ends with the number 955-04. Interestingly, the group 87.955 is referred to as 'Instrument equipment and special tools' (Geräte und Sonderwerkzeuge).
There is an opinion that these might be counterweights for balancing the aircraft after the installation of the additional armor set Umbausatz U3.
Does anyone here know where this was installed? Is this armor? Or any other information?
After scouring the entire internet, I've only found one similar photo:

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Excerpt from Ju87R-1 manual showing armour (Panzerung") locations:

Hi all:

My limited experience with German part numbers has been that anything that has a "R" in front is a cast part/or a casting number.

I just wonder if armour would be cast, rather than plate steel, heat treated, etc.

I'm making some B-17 armour, and if I read the drawings correctly, it is heat treated and has instructions on which way to install it.

Regards,
James

fshort said:

My limited experience with German part numbers has been that anything that has a "R" in front is a cast part/or a casting number.

Click to expand...

James, an interesting observation about the letter 'R.' I hadn't thought about it before, even though I often came across this marking on aluminum parts. For example, here's a part from the Ju 87's aileron: