Brake ID

[Omathisen]

Hi:
Trying to identify my front brakes and a clunking sound. I bought my ERA 10 years ago. Could not wait to build one or have one built to I bought one ready made. And that has been 10 years of fun.
It also means I do not know everything about the car.
It developed a clunking sound, when I brake. I went over the suspension, engine mounts, etc., but all seems fine. Instead the sound is coming from the brake pads that move and out in the caliper (when I rotate the wheel with car on jack stands). The sideways movement to the rotor is OK, but they are also able to move in the other direction -- in and out, up against a cotter pin, which makes a fairly loud clunking sound.
The calipers are Sierra (I assume from Sierra racing and not GMC?). But I have not been able to find a model number. In the ERA manual, at least the one I have, reference is made to GM calipers.
Did something fall off (a spacer or spring to keep them in) or is this a sign of wear?
Also, how do I open them up? The two big bolts on the inside?
I do not know much about this, but would like to. Some day when I am not working as much as now, the "plan" is to build my own car. Always good to have a plan for the future. Meanwhile, I have the brakes to figure out.
Thanks for any advice.

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