Rear Caliper Question: Missing the center shaft that Piston sits on

[IAN]

I'm in the process of rebuilding all my caliper on my 72 911T.

I pulled the rear calipers this eve and noticed:

One of the calipers is missing the center shaft (on both sides) where the pistons ride. These must have been broken off by someone deliberately at some point. They are broken off and almost smooth at the base.

The other caliper has these pieces in tact.

Are these center shafts needed? I believe there is a spring in the middle of the piston that grabs these shafts.

Any thoughts?

Thanks,
Ian