Has anyone swapped out their Sig 556 quad rail hand guards for the smaller polymer non quad rail versions ? If I could get rid of the cheese grater I might like the rifle

Yes, you need to look and see if you have a one piece upper rail, which extends over the receiver, or two piece.
If you have one piece, the sight / scope rail / rear sight will come off with the handguard.  You can either cut it and put the receiver section back on, buy MFI sights, or probably get somebody's take off rail from GB.
If you have a two piece one, there will probably still be an alignment tab that sticks out (forward) of the receiver mounted scope rail.
You'll need to either pull it out or notch your furniture.
I've got a picture of the later if that helps, PM me your email.

my brother swapped the normal hand guards for the quad rail. he probably still has them laying around

Hey, I just happened to do the same conversion on my 556 SWAT. Check out Optics Planet for the sight rail section if you have the one piece rail like I did. Sight Rail Link

And then check SIG's site for the Swiss style handguard (they still have them for $86) ... a bit spendy but that's your best bet right now. handguard

I'd be interested in those handguards if he's willing to part with them