well it will definately be somewhere in front of the cab mounting points
while you are setting up to do this-----are you planning/wanting/maybe to lower/raise the stance a bit??

I would suggest maybe to get some 2 inch channel iron, cut the frame perfectly straight in some area that will be easy to weld/re inforce on and move forward the 2 inches of the channel-

Prior to doing any cutting put some referance lines on in different areas so you will have points to measure, level, etc from

Take lots of measurements and record them plus these days lots of pics-------maybe get some lazor levels( I got more than a dozen) blocks shims clamps