Sorry I haven't checked it for a while so didn't see your reply, Fjallhrafn. That's cool you got a 601 with a 60's serial number, 0063 would be amazing or in my case 0068 since I was in Nam in 1968. Still, I'm glad to get a low number plus I got in before these rifles went out of stock for months. It seems Brownells is changing the anodizing. My 601 does mismatch a bit, the upper is a slightly greenish gray but that happened back in the 60s so not a big deal.

As far as magazines, I'm not familiar with the Brownells aluminum mag that comes with the XM16E1 since I got their retro steel waffle mag with the BRN-601. I believe you're right about NHMTG as I do have a couple 20rd NHMTG and a few Colts made between 2004-2009 with look very similar to a couple 1960s Colts and an Adventure Line and UI/Simmonds. My NHMTGs do have a rougher finish than the smooth 2004-2009 Colts and the '60s magazines.

I also have picked up a few M1 slings as they're useful for many rifles. One is a vintage seat belt type that's going on my 601 which has a long OD cotton sling now.