What to do with Colt 603/M16a1 upper?

[adriatic]

Found an oldschool Colt upper receiver at the gun show today for cheap. I was more in the market for a newer rifle build, but I couldn't pass up the deal.

I BELIEVE it's a 603/M16a1 upper, the guy didn't know what it was or where it came from. Barrel is marked C MP B; front site post has a C and bell. Bolt carrier has a "C", and forward assist serrations; bolt has "MPC". Teardrop forward assist; "CH" marks below rear site. It's in excellent condition - it almost looks unfired.

Any opinions on what I should do with it for a build? Nodak lower + oldschool a1 parts build? What other lower cost options are out there for a build like this? (furniture, lower parts kit, lower receiver, accessories, etc)

Or should I just sell it and build a newer m4 style carbine?

Excuse the shitty cell phone pics: