I'm using 5/8" Rancho u-bolts all around as well. Good stuff. <img border="0" title="" alt="[Cool]" src="images/icons/cool.gif" />

Bill- That's my trussed/shaved Taco axle w/ welded blocks:

<img src="http://home.off-road.com/~bibelheimer/images/temp/3-02_2/tacoaxle6.jpg" alt=" - " />
<img src="http://www.wildyoats.com/vbulletin/attachment.php?s=&postid=1633" alt=" - " />

The u-bolts pass through the truss, so that's probably what you're looking at. Details here:
http://www.4x4wire.com/ubb/ultimatebb.php?ubb=get_topic;f=11;t=006524

Someone asked me for dimensions of the plate-
They were cut from 1/2" x 6" flat bar
4.5" x 6" outside dimensions
11/16" punched bolt holes
2-5/8" x 3" inside the bolt holes (3" is the axle tube thickness, 2-5/8" is the spring width give or take)
The center hole is actually a slot 11/16" x 1-11/16" so you can move the axle up to an inch forward or backward (if you drill your perches to match), which is how I moved my axle back an extra inch.

HTH.