So talk to me about receiver flats.  I ask because I have been told that I would need one in order to complete an MP5 kit that Arms Unlimited has for sale.  Who has the best ones and who can build them?  I am an HK noob.

and then some.  You would also have to deal with the US parts count issue, even if you SBR.

As for bending the flat, you would need a press for sure, and a welder.  The barrel gets pressed in as well.  If you are good at mechanical type stuff, you could probably pull it off, but for the cost of that kit and the required parts, it might be easier to buy one already built (Zenith, Omega), or buy the kit had have it built.  Omega does offer complete receivers for sale as well.

It's not a simple build

Jason

If you're going the parts kit route. You'll be better sending your kit and flat to guys like, IGF or TPM Outfitters who specialize in building roller lock style guns and are awesome at it. If you go with a real HK kit, I'd send it to Mike Woodward at TSC Machine. He's one of the absolute best in the business but only works on factory HK guns, no clones. He is T/A runs around 3-4 months.

I'd recommend Jeff Walters of Parabellum Combat Systems.  He is Ghilliebear on HKPro forums.
http://www.hkpro.com/forum/parabellum-combat-systems/

If you decide on building yourself or getting your own flat the LSC flats are the best out there, just don't use the semi shelf it comes with. If you are thinking that building it yourself will save money I suggest you forget about that, and get a omega or zenith. I just built my first mp5 from flat and I am close to $2k in tooling, jigs and misc stuff items.

On the LSC shelf, can you just mill away the area that would normally be interfering with the receiver?

You can, the outer width is also a little wide and most clipped and pinned lowers would not fit over it. I use the ones from HKparts that come pre drilled with the paddle mag release hole, use the paddle mag jig to position for welding and voila, perfectly aligned and pre drilled shelf.