'Trigger plate action' is the term we're looking for here, right buzz?
The location of the hammer axles would seem to be the defining characteristic.
If the hammers ride on the trigger plate, and the bottom 'strap' or tang drops free from the rest of the frame during disassembly then you have a 'trigger plate action'. A 'Blitz action is a subset of that type.
If the frame (or 'receiver', same difference really) is machined in one piece and the lower tang does not drop out with the entire 'action' riding on it, then you have a boxlock gun. The hammers would ride on axles that would need to be driven out of the frame for disassembly.
I think. At least that's the way I've understood it. I don't have a Perazzi for examination.
