I know the 5/16 (Sorry, NOT 5/8) is 6.32lbs per foot and the solid is 13.6lbs per foot.
Edit: I just went and rough measured and it came out to ~16' needed not including the 1/4 plate for making the U-brackets and frame horn gussets/mounts.
Yeah... just figured out to ~216lbs total. You're right, she won't like that ExplorerTom although, a ranchhand is pretty heavy but not that heavy.
The 5/16 tubing would be ~100lbs of steel. I think she'd handle that better although a combination of 4' solid in the middle between the tow mounts and the balance in 5/16 would come out to ~130lbs which I think is reasonable.
Edit#2: Using solid for the whole main span with 5/16" tubing for the balance of the build would come out to ~148lbs.