Edge distance on WD-409 tail spring mount

[n567vb]

This may be more for the taildragger guys. I'm looking at the plans and it says the top AN4 bolts (on the foward plate) should be drilled 3/8 inch from the top of WD-409 tail spring mount. There's also a note to be careful about edge distance too. I calculate that the edge distance for a AN4 bolt should be 1/2 inch. Are edge distance for bolts different than for rivets?

Also for QB'ers, any tips on how to secure the tail spring mount while trying to drill it? I can't figure out how to get a clamp down in there. On QB's, the forward bulkhead (F-711) is already completely riveted in already and you have to drill the tail spring mount while intalled in the tail.

Thanks
Vince
RV-7 QB

 

[tcrv7]

The way the plan shows the bolt connecting the 409 rubbed on the center rivet below on the bulkhead that made the 409a1/4 high. turned the bolt over and gave good edge distance. The holes in the bulkhead where you drill I got it by having my dad hold it in place and marked it with a fine point sharpie.