FWIW I have the 260A / 300A HIMARS style brackets for $250. I had 15 of them made.
The HIMARS bracket fits the 260A but was designed for the larger and heavier 300A. They nixed the welded spring-board design in favor of a bracket that is bent from 3/8" plate and the only weld is for the pivot tube. Much more robust that the original 260A mount that has been known to crack at the pivot block weld and wasn't up to the task with the 98 lb HIMARS alternator.
Now whether these brackets will fit some commercial model like a J-180...... I'm not sure since I haven't tried that. I stayed within the Army ecosystem for my truck so I just don't have any to test with.....
View attachment 941984
View attachment 941985
260 vs 300:
View attachment 941986