Short night tonight...I drilled out these holes to 5/8 diameter for snap bushings.

Then it was on to match drilling the F-507D channels to the F-507E doublers. I noticed the six rivets outlined by the note, however I wasn't sure if that was meant for both the left and right sides or just the left side.

...so after some hunting through the plans I found that those holes are for the brackets that attach the canopy release mechanism to the rear spar bulkhead.

Hrm...since I'm going to be placing an order with Van's pretty soon anyway I think I'll order these two VS-411PP brackets so I can match drill them now rather than later. Hopefully I'll remember to have them omitted when I order the finish kit.