Will,

Never done one of those, but it looks to me like it would be simple enough - if you have enough of them to do. If sho, I'd probably look at turning a mandrel and spinning the main form, then adding the little cone-shaped boss on the very end. You'd need a break-apart mandrel, but that's no big issue.

Alternately, they could be raised and then have the end piece applied.

That end piece detail is the stumbling block to using flat sheet, so I'd definitely look at it as an add-on. Trying to start with heavy enough stock to leave that element and then work to thin enough for the remainder is going to be a LOT of work, unless you have a fifty-ton upsetter.

I'll be really interested to hear what others come up with for solutions - this is a pretty challenging exercise as I see it.

Depends how authentic you want to be, I would guess that the originals were forged down from a billet, though if the Nipple weren't solid they could have been spun.

at the time they would have had to make the sheet so it really wouldn't have made much difference to them.

Any how here is video showing a modern method using sheet;

http://uk.youtube.com/watch?v=bJxeFc-Nbb4&feature=channel

Click on the side to see all the videos leading up to this one.