I'm in the process of doing this to my '73 right now. It isn't too tough to do; just need to get all the parts. I found a good wrecking yard with some helpful people who pulled some barn doors from a donor vehicle and made sure to get all the little pieces. If you don't get all the small stuff (latches, hinges, rubber bumpers, straps, wiring harnesses for defroster & lock, etc, etc) the swap will nickle and dime you to death.
The one thing to watch out for is that you need to replace the lower sill assy. It has a recessed area that accomodates the lower latches, instead of the holes for the tailgate hinges.
I don't have it handy right now, but if you are interested, I can supply you with the correct GM part number for the sill. I think it cost about $200 from the Chevy parts counter, but can confirm that later also.
Just let me know,
Robb
<a target="_blank" href=http://community.webshots.com/user/robbrj>'73 GMC Suburban - 502DFI</a>