I'm seriously late to the party here, but I dealt with this years ago. I'd already read the Barton valve covers were made by Stage V. Barton rep confirmed for me.
I'd also read about cutting a T-slot (actually a V with a horizontal on top), push in, weld up on inner fender. Also welded up and redrilled shock mount holes. I had that done when I had the engine compartment painted.
Now I can slip fingers between pass-side valve cover and inner fender. Still close on heater motor, but fits.
I had this on Schumacher conversion mounts, then swapped to Devebic K-frame and original mounts. I'll look for the reference article I used.
Good luck!
Did your clearance issues go away after the Debevec k member swap? I originally thought that all of my clearance issues were due to the Schumacher conversion mounts, but even after swapping in a Debevec k member and stock style mounts, I still have the same issues but now it even hits the smaller manual steering box.
