[Worn Out Welder]

That looks like channel iron that someone fabricated to replace the factory perch plate which probably broke at the shock mount.
It might not be as bad with the factory radius rod that came on the 67s but….
Caltrains would be superior to most bolt on stuff

 

[Worn Out Welder]

Would it be possible to go with a multi-leaf since the perch plate has been fabricated? Won't the height be affected by a multi-leaf? (Sit higher)

They make a kit to convert mono to multi, and replacement lower shock plates are available.
I think ride height change would be minimal and most likely a little lower, but it depends on arch, condition and, weight.
I have stock replacement multi leaf( according to the Eaton tag) and they were a little less than the mono leaf.

 

[Worn Out Welder]

The OP pic showing the alternative perch wouldn’t need to be converted, and Caltrac bars replace the lower shock mount so this would just be a matter of the springs of choice and all bolt up stuff. 👍