off the subject kinda but does the c notch make the frame week at all? as in like lowering its payload capacity?
As long as it is boxed in and your welds are good, you'll be fine. If you're still nervous, just plate it.
Im running 4" drop blocks with stock bumpstops in the rear of my 76 longbed and havent had any issues. My truck is monoleafed as well.