So….heres my theory:
If the conventional mounts fit the Big Bolts, then those HD mounts probably fit the 1/2 ton Bolts.
As weird as they appear, if you study the assembly diagram in some of those eBay listings….its two bolts horizontal into the bell…and one bolt vertically into the frame. Just like the conventional ones.
If they weren’t so daggum expensive, I’d buy a set just for science.