Plan instructions say typical cabin is 42 1/2 and you should reduce the roll bar width by 3/8 making it 42 1/8. My cabin is 42 7/16 edge of longeron to edge of longeron so I made the roll bars 42 1/16 wide. Triple checked that measurement plus the height at 17 7/8 and clamped it down and match drilled the splice plate which I pre drilled earlier. Take note of the tooling holes to be sure you have good clearance for the AD4 rivets. Repeated this for the aft section halves. Marked 1 1/2 inch rivet spacing on all flanges and drilled them to #40 for starters. Did not drill the lowest holes yet until I understand how that the F631C and F631D attach angle bolt and screw holes interact. The aft section of the F631A attaches to the joining strips with CS4 rivets. They are 120 degrees so I ordered a120 degree piloted countersink and dimple dies from Cleaveland Tool, plus bunch of other stuff I need. Plan says CS4 flush rivet heads are thinner and will adapt to the 100 degree countersink, but why chance it.
Assure yourself you have a flat working surface. Cleco right into the pressed board.
My measurements. Your's may vary.
Plan says to have joining halves touch eash other. Not always possible, but I came real close.
