[dsraven]

yup, do the grind at the section where the front meets the back but before you start anything ensure the frame is sitting square and level. put some tape on the crossmembers and mark the centre, side to side, then when you run a string or laser from the front to the rear all the centres should line up. also, put some tape with marks on the side of the frame so when you are putting it all back together you will be able to reference those marks to make sure it is level and not sagged in the middle. make some centre punch marks on the frame rails on the front and rear sections of both halfs (before the grinding) so you know how much you are moving each side. make sure they are far enough apart so they won't be pushed up inside when you slide the rear part into the front part. don't forget to take the fuel lines, brake lines, wiring, park brake cable exhaust and driveshaft into consideration before shortening. is the frame bare without engine and trans or is there gonna be stuff in the way? a corner to corner measurement is a good thing to take as well, but hard to do with stuff in the way. take your time and measure lots. better now than when you are all done and the front end guy is having a hard time getting an alignment done. also, you should actually replace the spindles because they may have a different part number for a longer wheelbase compared to a shorter wheelbase. google "ackerman angle for steering geometry" and you will see what I am talking about. it may or may not be a big deal. you could always check with a dealer to see if the part numbers are different.
have fun and post some pics so we can all "bench race", ha ha.