What you have is an early version of the WE MEU(SOC) .45 1911, with the [mostly] correct Springfield markings, modelled after the MGC GM5/Western Arms MEU(SOC). It's modelled after the circa ~2003 production of the MEUSOC pistol with COTS Springfield Custom slides with the forward serrations added by Quantico armorers (front right of the slide, behind the serrations you'll see the cut off SPRIngfield CUstom).
Later versions of the WE MEU were either blank or had bogus USMC markings. You also have correct Pachmayr medallions on the grips (Pachmayr model GM-45; real ones fit, too). Later models either sport a USMC EGA or the WE logo on the medallion. All iterations of the pistol were known as the MEU 1911 and are the same gun except for the markings (the early version with correct trademarks was actually sold by WE, not HK3).
The paint was removed, not worn off (there are bare parts where it wouldn't have worn).
For the slide lock, any WE 1911 one should fit although if you want to keep the MEU "kosher" you should use the non-extended one. Not sure if the TM/KJW replacements will fit (they look the same but I never tried).
Depending on how accurate an MEU clone you're looking to build you may need to perform a few other tweaks.
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