The rear deck will sit on top of the back edge of the seat back.

Very cool Ray,

How do you finish off bend, so there's no srarp edges on the back side of the bench?

 

A little more on the bending and the grain structure, in a piece that has a radius bend like the dash and seat back, as the Aluminum is being hammered over the wooden form it is hardened due to the deforming grain structure and the flange being formed will pucker and not lie flat enough where the Aluminum actually needs to shrink. I will have to anneal the flange to soften it so it can be hammered flat. I judge the temperature by marking the flange with a permanent marker like a sharpie and heating it with a torch until the marks disappear.
First photo is the wood form being fitted to the boat.
Second photo the wood form is actually under the Aluminum and the wood you see on top is a backer to keep the Aluminum sheet flat up to the edge of the bend.
What you don't see in the photos is the big dead blow plastic faced hammer and the vicious hammering it takes to move the Aluminum. The eight big C-clamps are not enough to keep everything in position, there are 4 screws going all the way through the wood and the Aluminum sheet to keep everything in place. 

All metals have a grain structure and it very much determines how strong and how ductile it is, just like wood, metal will brake much easier along the grain.
I make wooden forms to bend pieces like the dash and the top edge of the seat backs.
 

That's right, I forgot the rear of the boat has a deck too. 

Grain structure on aluminum, That's a thing?
Must be like wood.

How do you bend those large radiuses on the dashboard?

New seat back, dash, and old bulkhead beat back into usable condition after whoever cut this thing up had their way with it.

 

I buy from a welding shop in Knoxville about twenty miles from here that I have been doing business with since the early eighties. The dash, seat bottom and seat back are all more than 4 foot wide and the grain structure runs long ways with the sheets so you really need the 5 foot wide stuff so you’re bending across the grain and not along the grain, I have always used the 5’ X 10’ sheets, I must have made six or eight dashes over the years. The Rocket has a one piece front deck too and I hope to get both the front and rear deck out of this sheet.
I already have the seat and the dash for the Rocket made from another sheet that I had already cut a different dash out of.
I cut everything that has a curve or is too big for my little 32” shear with a jig saw. I do trimming and little cuts with aircraft shears, that will keep your handshake firm but I guess handshakes are obsolete now.

Dang 5x10?  Hopefully you didn't have to drive far.

Where the heck do you buy something like that?

Okay so what's it going to be used for, the deck? what else? That sure is a big sheet, what do you use to cut it with?