I am really into the retro AR thing!
Have any of you guys tried this? Can I mill off the mag fence & detent pin retaining protrusion? Does anyone sell a Lower lkike this? will a custom shop build one of these for me?  

garr...Getting into the retro-look, eh? Yes, there are quite a few of those retro type lowers for sale. They were made between 1957 & 1992 and cost anywhere from $500-$1,500 USD each.

Have I, or do I know, anyone that has shaved/milled their supports off? No.

Can you do it(BIY)? O yaa shoore yoo betcha. As long as you don't attempt to assemble your rifle as PRE BAN, that'd probably fly. Otherwise you'll be looking at "getting into" a bright orange jumpsuit, a pair of gellies and you'll be sporting some really swanky nickled plated jewelry. You could pay to have a Class2 manf'r build you a serial'd no fence/no strut lower. Try asking a licensed builder in your locale...Bud

Because we can

The reason I wanted to use a post ban lower is because if it gets screwed up big deal, I will simply try another! If a pre ban Small holelower gets screwed up it is gone forever!

I have a couple of pre-ban Colt SP1 type rifles with slab sided lowers, The problem is they are all large hole! I want a small hole to replicate a very early rifle.

Also I am aware of the law with regards to pre-post ban assembly requirements, I have no intention of doing anything that is not legal,
I intend to use a custom 1:14 inch twist barrel with the bayonet lug neutered with a permanently attached Fake duckbill F/S from Kurts Kustom to give me the retro look, but still follow the letter of the law!

garr...I take it that you are not keen on using adapter pins. Is this going to be a wallhanger or a shooter? If it's a wallhanger then write me with an addy that I can send PIX to...I have something that'll make ya weep. I copy on not wanting to trash a lower. Find a smith in/near your locale & ask away. Ever consider buying a lower casting and building it yourself? Just a thought, eh...Bud