First build from the ground up, so I have raw aluminum parts---which means there are still machining marks.
I have been putting this off, because the prospect of sitting down with some 1000 grit sandpaper is not appealing.

Any easier suggestions?
1. Get someone else to do it
2. Drop them in a tumbler
3. Dremel
4. Quit b____in' and get the sandpaper
5. Don't bother..............I am planning on Duracoat

Yeah pictures would help.  If they aren't too bad,  might be easiest to just Cerakote over them. 

Yeah, those are pretty noticeable.  I don't think Cerakoting would hide them.   

Oh ok,  they look like they are more raised, but that might just be the picture.  You could try putting some cerakote on a small section of the magwell and see if it hides it.  If it does, just do the whole thing.   

This. ^   Hand sanding is a royal pain in the rear end even with shaped blocks and slip stones.  If the final finish is going to be ceracote you don't have to have everything looking like a mirror but some continuity in the finish from one spot to the next is good.   

I have a sand/bead rig.  But I am not particularly close to you.  Planning any travel to SLC?

Or.  If you have an air compressor, get over to harbor freight and grab a cheap blast gun ($20) and some media.  You don't have to have a cabinet for one lower.  I will also comment that this can be slow as you have very short duty cycle with the typical pancake compressor.