I was reviewing the pictures of the original benches as I was laying in bed (look I get a bit obsessed at the start of a project) when I noticed that I had missed the substantial seat overhang on the ends of the bench. After a bit of SketchUp work I decided on 3.5 inches of overhang on each side meaning my original seat length was 6 inches short. Luckily I had been unable to decide on a grain pattern so I had not cut the board yet.
The extra 6 inches of length set the grain pattern so I felt confident making my rough cuts. Planing this thing is going to be a frustrating experience with tear out. I also managed to square two edges on the pieces for the base (the seat needs a week in the shop to acclimatize) so hopefully I can set up the planer sometime this week.