I did it on mine, although mine was a long bed cut short the wrong way by clipping off only at the end and moving the rear end up. I corrected this jerry-rig by locating a shortbed frame and welding it in place starting under the cab.
By cutting in the middle and on the end, you are effectively removing all the longbed sections and just leaving a shortbed frame so yes, the stock mounts will be in the right position. Here's my conversion:
http://www.grossepointegothic.com/71stepside/FrameSwap/
Don't forget the Frame Stiffener Support from Early Classic. Might want to consider bolting them in too, I welded mine and hmmm, I see it is going to make removing the crossmember difficult, it not impossible if I need to pull the tranny.