If you look closely at the bottom of the pad you can see circular uniform cutter marks from a horizontal milling machine like a Storm Vulcan Blockmaster etc. Stamp appears to have some inconsistent fonts when comparing it to known originals I have, it also looks like it has been sandblasted judging from the pad patina. I don't think personally it is a original. IMO.
Here is a Real Pad from a LA Z28, remember that engines were all built at Flint, engine id stamps should be the same. vin stamps were added at the assembly plant.
Also another real 2 days later, not a Great picture though, Sorry.