Dating an SP1 upper?

[Lee Enfield]

[QUOTE=garrettbragg12;353820]I got bit by the retro bug and while building an M16A1, I picked up a SP1 stripped upper. I looked at a few sites but I'm still confused on whether or not it's an early or late upper. It makes a huge difference on the parts used on the build! Thank you!
QUOTE]
It appears to be a fairly early Colt upper. Later uppers had letter codes in the right side webbing under the rear sight.
Attachment 69193

It looks like you have faint Colt inspection markings, similar to this:
Attachment 69192

Is that an SP1 upper, or an early AR15/XM16 upper?

If the front pivot hole is .250" it's AR15/M16, if it's .316" is SP1.