G'day vint_mow,
I'd strongly suspect that those tabs would have a 'double bend', as in fig 5 of this article: http://www.thefabricator.com/article/stamping/know-your-bending-basicsaeuropart-ii
That way they would 'hook' into the chassis slots, to retain the windrower in position.

In the absence of a die set to press form these, it would be easy enough to fab up a simple bottom former from a couple of bits of flat mild steel, and just use a hammer and a square drift to cold form them.

In my case, I'd probably just use the step between my anvil's cutting table [the small flat at the base of the horn] and main face as the former.

[Linked Image]

Cheers,
Gadge

"ODK Mods can explain it to you, but they can't understand it for you..."

"Crazy can be medicated, ignorance can be educated - but there is no cure for stupid..."