You could also look for a Ford 9" out of an early bronco, you would have endless possibilities with a 9".
Just for your comfort, there is a guy up here in WA who runs around in the sand dunes, he has a 2wd Yota, 3rd gen, 350 SBC, Auto Trans, and a total chaos kit, using the stock rear axle, that is welded, he has not had a problem yet and he smashes on that thing. 
I have several friends that have those "Shoe box Bronco's" and from what they tell me 98% of them with the 9 inch rear ends only have 28 spline axles so they are obviously the weak link.
You could up grade to the 31 spline but it will take some $$$ to do. It does not suprise me that the Toy rear has held up.
I am a firm believer that those axles "will" take a tremendous amount of abuse!
