I've been wondering the same thing since I may need a u-haul to go get my 78 J10, and it's 240 miles away.
Looked in my shop manual for 78, (I'd assume 77 would be the same) so here's some specs, "original" specs anyway for the J10.
w/b 118.7 or 130.7
overall length 192.5 or 204.5
front overhang 29.9
rear overhang 43.9
overall width 78.9
front tread 63.3
rear tread 63.8
Well after typing that I'm not sure what the width would be on the outside of the tires.
I's think the overall width would include the body, and the front & rear tread would be from the center of each tire.
So basically all this information is useless!
You should probably have someone measure it to be sure, sorry!