Assuming "the soundboard will have to be trimmed" means "do it now," I set out to trim it down to size. The instruction manual does not offer any hints on how one might accomplish that, so, taking no chances, I elected to use a cardboard template, an X-Acto knife, an Exacut with the wheel cutter attachment, and sandpaper. The first thing I did was trace the shape of the soundboard onto a piece of cardboard and cut it out. At that point I was able to slowly trim the straight "north" and "east" sides of the cardboard until it fit the case perfectly. I then laid the cardboard template on the spruce soundboard and drew lines where the soundboard needed to be trimmed. Laying a long metal straightedge along the line on the right ("east") side of the board, I cut a scoring line with the X-Acto knife.
This cut went across the grain, so after cutting a good deep score, I switched to my Exacut with the wheel cutter attached to it and deepened the cut until it went through to the bottom. Perfect! I repeated the routine on the top, or "north" end of the board. Since I was cutting with the grain, this took a fraction of the time. The board was still (purposely) a hair too large, so I sanded the two edges until it fit perfectly.
Confession time. When I glued the long hitchpin rail, I didn't notice that it was a fraction too long. Two possible remedies: try to trim/sand it or cut a small notch in the soundboard to accommodate it. I chose the latter, and it looks fabulous!
