There really is no cutoff nor are the numbers sequential- it wasnt the first 500
It was however about 500 of the first 1000 although there were a handfull spread throughout the second thousand.
The receviers themselves were made on equipment that just wasnt up to the way Germans were used to doing things- that equipment was for the most part shipped over from the US
The parts you find in these receivers often are remington parts
I am not sure if there was any difference in the actual alloy but many of these receivers over the years have been fooled with by different gunsmiths
All of those receivers can be updated but it often requires welding and reboring because the geometry and tolerances werent the same-- it really takes a CNC type process to make them interchange
Hinge pins-- as far as hinge pins- I havent personally seen the smaller hinge pin on the K32s but the Remington 32s had both large and small hinge pins- depending on age
I have actually had a highly engraved Remington converted to K80 parts by Ottsville and it did require the welding and re machining to make this work
regards from Iowa
Gene