Link to Ed Browns:
http ://www.edbrown.com/cgi-bin/htmlos.cgi/00500.1.571917813261510374
http ://www.edbrown.com/cgi-bin/htmlos.cgi/00500.2.2029198971461510374
It doesnt mention the angle, but I am sure if you install one on a gun it will be pretty obvious what needs to be cut and where to put a new hole for the Mainspring Pin.
The Executive Carry is essentially the Executive Elite modified for carry. It's the solution for those who prefer a smaller model 1911, but insist on complete reliability. The slide has been reduced to the minimum possible (4.25") without significantly impairing the legendary reliability of the 5" slide. The frame has been modified with the innovative Ed Brown BobtailTM housing which reduces the projecting butt of the mainspring housing without sacrificing the full size frame and magazine capacity. The BobtailTM minimizes the print under your jacket when carrying and reduces weight. Officer's frames reduce magazine capacity and limit grip, while keeping the projecting, sharp butt. Slides shorter than 4.25" are notorious for reduced reliability. These problems are eliminated with the Ed Brown Commander BobtailTM configuration, which reflects the genius of John Browning with an innovative modern flair. The functional simplicity has yet to be matched. Unique with the Executive series pistols is the 25 LPI checkered frame and "half checkered" BobtailTM. This pattern is not too rough on the hands, but not too fine for a secure grip. The Executive Carry is truly at the top of it's field. Get promoted to an Executive Carry - it's a serious tool for the competent professional!
Link to Brownells for the Housing and for the Jig.:
http ://www.brownells.com/aspx/NS/store/ProductDetail.aspx?p=1346&title=1911+AUTO+BOBTAIL+MAINSPRING+HOUSING
Eliminates the sharp profile at the rear of the grip that can “print” when carrying a concealed 1911 Auto. Reduces bulk without reducing magazine capacity or performance. Removes nearly ½" of material from the butt while maintaining correct grip position. Will require modification of grip panels. Choose from Smooth, Checkered (25 lpi) or Snakeskin patterns. Installation Jig gives precise location of mainspring hole.
Sorry I couldnt find anything on the actual angle, I suspect the jig would be the best way to modify your own frame and avoid any issues.