Layback seatpost for 56 roadmaster

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I’ve got a 56 roadmaster with a quill stem style seatpost. I’d like a layback seatpost. Is this possible?
 
A quill stem is the right idea, but maybe not so good in practice? Finding an acceptable stem with the proper reach might pose a real challenge. I'd probably lean toward using a genuine layback post and modify a BMX-style clamp for the job. Just a suggestion.

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I think the 56 AMF Roadmaster frame won't have space for a clamp in the usual spot. I think the post i's 13/16ths width so a layback stem will be hard to find in that size, probably 7/8ths or larger is all you will find. If you do find that size, a layback post would work with some fab work.
You could use the quill stem that came with the bike and make up some kind of extension bar that would clamp to it, and extend rearward that the seat would then attach to somehow. That would take a little engineering.
Or use a layback seatpost that is fairly long so it would be inserted about 4 inches into the frame and still be tall enough for the height you want. Then cut a slot in the frame about 3 inches long and 1/8th inch wide vertically just below the junction of the top bar and stays, on the rear portion of the seat tube. Don't cut a slot all the way from the top, start below the junction point to keep the integrity of the frame. A dremel or some kind of small grinder might be the best way to cut the slit. That's where the seat post clamp will go to tighten the layback seatpost, under the juction of the top tube and stays. The clamp would go halfway down the slot to be able to squeeze the tube enough to hold the post. It would be like the usual way a post tightens but be lower on the frame.
In reality, that size post probably can't be found in a layback style. An extension off the original post is most probably the only way to do it.
 
Double-bolt clamp to the rescue...maybe. A shim, like the one pictured, will likely be in order. I just measured my '54 Shelby w/ quill seatpost and its seat tube extends about 1" above the top tube. If your frame is similar, then there may be enough 'meat' there to install a traditional clamp.

I also checked eBay for 13/16" layback posts. While they weren't plentiful, they weren't exactly scarce, either. Prices hovered in the $15-25 range + shipping.
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