This part comes as part of the F704 center section assembly, matched drilled (as I understand) as a set with the F704 E/F center section halves and the wing spars.
Check with Vans on this; this could be a difficult add-in after the fact. Two AN4 bolts go through this block to the wing spar web nutplates. Something needs to go in there to act as a spacer.
N430WB (reserved) RV-7 #74152, tip-up. Avionics and FF underway!
Log at: http://rv7.wbencze.com
Defeating gravity one rivet at a time
VAF 2017 donation happily made