Just happened to check the KC Craigslist, and someone has a 1957 Sportster for sale. Suppose to be in 'Great Condition', and from the pictures it looks like a beauty... (Link Below)...
This is the first year of production, and you don't see many of these for sale, especially one that appears to be in original condition....
I might have to make a little run up to Olathe KS and check it out..
The Sportster XL was introduced as "a modern, up-to-date power plant."
55cid 7.5:1 Compression, hemi-spherical style heads, 90 degree valve angle, 4 cams
XL (1983), $1,103
(Pictures of bike for sale)