I added a page tonight for the Colt Prototype SP901/LE901 Upper Receiver. You can see detailed images here: https://thecoltar15resource.com/colt-prototype-le901-308-upper-receiver/
The Colt AR-15 Resource
"A site dedicated to the history of the Colt AR-15 rifles, carbines and associated items"
The Colt AR-15 Resource 