Re-Barreled late 80's Savage 110. Originally in .243 Win, now in 7mm-08.

Who is a good option to send receiver off to for machining to allow magazines to seat in a chassis?

or -- do you think it's safe to just hot it out with a dremel :)

Do you already have the chassis? I think its chassis dependent, but I thought most chassis were pretty plug and play.

Yes, I have an MDT Chassis. It fastens fine.

I knew I was going to have to do some machining because the magazine port is for short action, but the action screw spacing are for long action.

No one makes a stock with long action screw chassis screw spacing, but a short action magazine broach that is correctly positioned to feed cartridges....at least that I can find.

Do it yourself with a dremel.  Extend the existing line of the mag well to the point where you look across the bolt face pulled fully aft through the mag well and see air.  
If you get yourself an AI magazine you can also fit it into the well so that it slides in and fully touches the bolt when the bolt is closed..  All metal is removed from the AFT portion of the well.  Very easy to do and you almost can't screw it up.