I hope this is the right place to put this.

New to the AR platform and the forum here. I have designed and built some single shot falling block pistols before, and years ago built up my bolt gun from a VZ-24 mauser action, so I am not totally ignorant of firearm work. I recently was cleaning up the shop and came across a 0% forging that I got during the Clinton era scare. I am in the process of milling it out and it is going quite well… so well that I am thinking about doing one from a raw chunk of aluminum.

I am not well acquainted with the platform. We didn’t get/have to play with the Mickey Mouse guns when spent my 2 year paid vacation in the Army. On the right side of the magazine well there are some raised sections. One of them is for the pivot pin retainer, but what are the rest of them for? My guess is that they provide some protection from accidentally depressing the magazine release while slogging through the jungle. But, is there a structural reason? Can I get away with just milling the magazine wall flat (except for the pin retainer, of course)? Manual milling the little curved sections is a pain

Larry

Thats exactly it, its just for keeping the mag button safe and less material = less weight

It's called fencing. It was added to the lower to prevent the mag from being released.
You can mill it off, but I don't see a reason why. You're not losing much weight.

If you are, I'd do it like this:

Or you can just buy an early A1 lower that lacks the mag button fence.

https://www.brownells.com/rifle-parts/receiver-parts/receivers/lower-receivers/ar-15-xm16e1-lower-receivers-prod105044.aspx

Defeats the purpose of wanting to machine your own lower out of a blank block of aluminum if you just buy one.

Build a glock lower and polish the hell out of it

That would be different.