You don't need to find one------- I've got what you want right here. Make me a reasonable offer on the crank and rods and they're your's. I got them cheap just rescued them from the scrapper.
i think they were available in f-450 and up trucks, basically anything commercial, the basic idea was long stroke for torque and small bore for better fuel economy, i used to drive a gmc top-kick bobtail that had a 366 big block chevy truck motor and i beleive those had steel cranks as well, but i don't remember if the stroke was 454 or 396
I don't know where the long stroke part comes in. The 3.59 stroke of the 429 isn't hardly what I'd call a long stroke for a big block. I don't know what Ford was thinking here, except maybe an extremely high rod/stroke ratio.