It should be do-able fairly easy,you'll probably need to either move the rear cab frame mounts ro the proper spot for the 66 cab,might need the mounts from the 66 frame to work,or make custom ones...a body lift might be needed to clear the transfer case on a 2wd if the tranny hump wont clear it...or you could modify the hump taller..
I helped a guy put a 55 Suburban 2wd body on a 77 GMC K1500 chassis and it was a lot less harder than we figured it would be...ended up with a nice old 4x4 Burb with a cool body style for not much money back in the 90's when he found both at a scrapyard waiting to be stuffed in the crusher,he paid the place 800 bucks for both,double what the scrap price was back then...we used rear the frame mounts off the Suburban frame...at first he was going to just put the t-case on the 55 frame and replace the straight front axle with the 4x4 one,but then we figured the disc brakes and power steering were well worth having,and it really wasnt a involved job making the cab mounts work on the later frame...
