I’d make it wider. I’ve been working on my regular topper here:
I discuss this towards the bottom of the first page.
If you want 4 inches extra on each side of American Landings you’ll want 53 inches wide. For British landings you probably want that section 57 inches wide. The double board Gold-Omaha takes 57 inches wide by 56 inches and is the worst board short of the 7 foot long Normandy. So if you want one big board minimal size I’d go is 7 feet by 57 inches. For Gold-Omaha there is enough room on each side for the players to cut it close. I’m going to have to shoe horn mine in a bit more and will just have cardboard sections that tightly inset my current topper that extends my table width to 42 inches.
I’m still hatching my scheme, but my space is so tight around the table that I can’t do the above. I’m probably going to make custom sections that are all 28 inches wide with varying depths that jut out one side of the table or the other. I’ll probably have Gold-Omaha so these pieces just fit the board leaving the game players to sit before the board where it indents.