What to do with Colt 603/M16a1 upper?

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:

slap it on a lower and use it as a varmint gun. those 1:12 pencil bbl's are excellent shooters using 55 and lighter grain bullets.

i think its a peice of junk and you need to bring it to papa[ROFL3] just alpha duece that mother effer out

Not a 603 upper. It's a big pin SP1 upper someone threw a set of A2 handguards on.

Still very nice, and many of the parts are period correct, by all means do a retro build.

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Originally Posted by Circuits

Not a 603 upper. It's a big pin SP1 upper someone threw a set of A2 handguards on.

Still very nice, and many of the parts are period correct, by all means do a retro build.

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I see, so that makes getting a lower more difficult, correct? What are my options?

edit: What makes it an SP1?

SP1- Colts original civilian version of the M16. Identical to a .gov 16 less the happy switch. Colt did a few things to make it non compatible with military parts:
Hardend block in the safety area that is blind pinned to prevent FA fire control parts.
Larger trigger and hammer pins .170 vs .153 (IIRC) for the same reason noted above.
Larger front takedown pin to prevent a mil-spec lower from just dropping on.

Colts attempt at being PC.

Fitting it to a late model lower is no problem, you just need offset pin bushings or an offset pin.

A1 build- Vietnam era rifle.
Old skool cool.

The Nodak lowers are nice. I would do an A1. Everyone wants an M4 style.

I do not care for them. If I want short I just grab my Izzy A1. [Beer]

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Originally Posted by BPTactical

SP1- Colts original civilian version of the M16. Identical to a .gov 16 less the happy switch. Colt did a few things to make it non compatible with military parts:
Hardend block in the safety area that is blind pinned to prevent FA fire control parts.
Larger trigger and hammer pins .170 vs .153 (IIRC) for the same reason noted above.
Larger front takedown pin to prevent a mil-spec lower from just dropping on.

Colts attempt at being PC.

Fitting it to a late model lower is no problem, you just need offset pin bushings or an offset pin.

A1 build- Vietnam era rifle.
Old skool cool.

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So if I grab a Nodak lower, or any other modern small pivot pin lower, I can build it with a regular parts kit? (i.e. a regular Spike's parts kit?)

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Originally Posted by adriatic

So if I grab a Nodak lower, or any other modern small pivot pin lower, I can build it with a regular parts kit? (i.e. a regular Spike's parts kit?)

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If I remember correctly put the bushing in the upper and then all the normal parts will work. I used a normal DPMS LPK on a nodak A1 lower mated to a GI upper. everything fit fine.