Correct term is lug slotting. A1s were slotted for the lugs on the Unertl scope base. Hand fitted. Original M40 receivers that had stripper clip slots would have been converted to A1 specs. There's a diagram out there showing how to mill one in the receiver. Don't believe it's too difficult as long as you know what to do as a smith.
Several different barrel manufacturers were used during the lifetime of the A1. Since this is a clone it depends on what timeframe they were looking to clone. Schneider would have been late 90s time frame. Basically rebarrels at that time before being converted to A3s. I have two rifles built on Schneider barrels and one actual contract barrel I haven't used yet. There is a difference in all three in regards to the rough finish he left on them. One of the barrels I cerakoted and it still can be used as a file. The other two are not as rough. The barrel used on my A1 clone looks like yours. Still some roughness on the barrel but whatever was used as a coating covers it up. It is not black oxided as it should be.
