A friend of mine dropped off a barrel with front sight and flash supressor, forend and gas tube from an SP1.  I have been looking to assemble an older vintage AR for some time.

What other special parts will I need?

I know I need a slab side upper.

I know I need a chromed bolt carrier and forward assist serrations are actually period correct. (That is what originally came in it)

I know the rear stock is different than the current versions as well as the grip.

What about the lower?

I looked at the sticky thread here with different versions but a lot of it started at the M16A1 and I know that isn't right for this deal either.

Thanks for the help.  

The lower is also slab sided, no mag fence and no A2 reinforcements near the front and rear take down pins.  Sp1's also came with a normal bolt carrier, but the lower half of the rear is a special length.  I think the early ones might have come with a chromed carrier, but mine is a '68 and it has a bolt carrier with forard assist.  Grip is kind of like an A2, but it doesn't have the finger groove.  I beleive the stock could have been either the M16 style for the first ones, and A1 for later guns.  Differance is the A1 have a trap door in the rear and a non-swivel sling loop.