I did something similar, but just used a 200mm nodal slide (I wanted mine to be >5" from barrel, so I chose the 200mm), popped the bubble level off, and mounted a similar Sunwayfoto SPC-50 (clamps to both arca and picatinny for $35). I did have to get a 1/4-20 FHCS as the Sunwayfoto came with a...