What is this?

Looks like autopilot controls to me.
 
STec ST-360 altitude alerter, DH alerter and vertical speed controller. I have one in my Arrow.
 
I believe the one below is the main “head unit” of the AP. Do a search for the STEC manuals. Logbooks/STC should explain what was installed.
 
Thanks, how does this differ from the Stec controller that is lower in the stack?

I am no expert, but I am pretty sure that the unit below the one that is circled is a Piper AutoControl IIIB (same as Century IIB). Not an STEC. The 5 position rotary switch in the center of the panel is the mode selector...

I can't help with the circled device. Sorry

^^^ This.

Your autopilot is an analogue Piper Autocontrol IIIB/Century IIB (just below your circled item). It's a single axis autopilot with heading control (Nav/LOC) through the HSI.

As @Arrow76R noted, your circled item is an ST-360. It's an "add on" box that works with the Century IIB autopilot to provide altitude alerting/altitude hold and vertical speed.

The Century IIB is still considered a pretty good autopilot and there's good support still available to keep them working properly.
 
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@GRG55 is correct, but to be completely pedantic the add-on capability comes from the S-Tec 60PSS (below the IIB), which adds the second axis of control (alt hold, VS and GS capability) The century IIB remains the lateral control system. The ST-360 then adds-on to the 60PSS to add alt preselect capability and better VS control.
 
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