Whilst copying pics of the trigger guard differences, I also noticed that Wilhelm's M40 has the hexagonal barrel flange (mine has the round flange)...
You can see that the trigger guards are machined differently; it's not just an elimination of a machining step...The opening in Wilhelm's guard is larger...
Mine is all-matching; "arsenal refinished"; bought back in the late 70's/early 80's...Surplus, parts were abundant...Spare slides especially...I bought a spare slide/bolt...Lots of rumors about the slides cracking; I've never seen one cracked...