Steampunk look/theme would be damaged by anything close to the stock seat. I'm unable to picture a foam padded seat.

http://www.jpcycles.com/product/504-139?utm_term=%5B74946362770%3Aproduct_typ...

It's a step in the right direction, but still too modern.
A well shaped, properly sized Buttcupping sprung saddle, along with the suspension, I would think would still be comfortable. I really don't Know that or If such a saddle can be found that matches your bum. And No, I don't think you should post pictures of it with a tape measure so we can try to find the best fit.

I'm not annoyed Pesci. But, it Is kinda annoying that you would think so.
IDK what a seat like that would weigh, just be aware that a sprung seat Can compress the springs and fly up to spank your butt.
If you're butthurt because I didn't wanna see pics of yer bum, Well, sorry Dude, but , you Are a dude..
Annoyed,, how annoying,  

The tractor seat just doesn't look right, To Me.
The tractor seat and Steampunk look might mix, IDK, but my minds eye sees a leather saddle in a chrome frame.
Annoyed, Ha!

An attempt at humor that evidently didn't translate well..

Awbveeuslee...

C'mon, Pesci, you know I like you, just, not enough to wanna See exactly what you're trying to fit into the saddle.

So, a couple decided to tour France for their Second Honeymoon, the ten year anniversary.
Everywhere they went, no matter what they ate, they wound up doing double doody, lots and lots of toilet paper getting used. When they got home and told their tale, a wise friend summed up the moral of the story.

With France like that,
Who needs enemas?

Thought this build was going to be in the board track vein?

http://sportsmanflyer.com/

Or modify a Brooks bicycle seat.  (All the hipsters use brooks. )

http://www.brooksengland.com/en_us/

I'm with Dave on this one ,the tractor seat sides will lock your legs into a forward position not allowing you to put your feet down to the ground ,unless you use a metal seat (steel ) that would allow you to cut the forward sides down. the cast iron seats shown are worthless as cast can't be ground down and is easily broken on impact.(not good for the butt,or as Mr. Rogers use to say ,can you say laceration? Sure you can! )

If your wanting a steampunk look I would stay close to dark/rich woods, leather, brass, and copper.

If you can't find what your looking for make it, custom doesn't mean store bought. It doesn't take much to make a nice saddle from scratch.

The one I threw together has a 3/16th thick aluminium pan, for the foam I used multiple layers of anti microbial yoga mat, and the cover is a high quailty 7oz. saddle (horse saddle) leather. This stuff wears like an old baseball glove and will most likely outlast the bike if mildly taken care of. This particular saddle is hard mounted to my frame using the stock front clip and two bolts, but a swing bracket and springs can be used just as easy.

Thanks Lancer, it was put together with a round braid using 1/8" calf lace.