The only machining I've ever needed to do on AICS chassis is to open the trigger pockets for a Jewell or open the recoil lug slot for a thicker recoil lug. (Also bolt handle relief mods for a Surgeon action, but you're talking about factory R700 actions.)
The newer AICS stocks have a wider recoil lug relief milled into them that will fit most oversize recoil lugs but AI hasn't made any alterations to the trigger pocket. A Jewell trigger requires a couple of areas be opened up in the AICS for clearance while a Timney trigger requires either a small groove be machined in the AICS for the pin that pokes out of the left side when the safety is engaged or you can slightly file down the protruding pin on the trigger itself and then it will fit in the AICS as-is.
I'm not saying AI is immune from any problems but if there's a fitment issue I'd tend to believe it's a Remington issue-- there have been one or two posts here recently of guys with poorly installed/clocked recoil lugs and misdrilled/tapped holes on new R700s, if they poorly finish the bottom profile of the receiver it's going to have issues fitting in the stock.
