I believe the Sportster was first produced in 1957, making next year that model's 50th anniversary.
Here's a good page on the Sporster evolution: http://www.sportster.org/history/
1957:
[highlight]The Sportster XL was introduced as "a modern, up-to-date power plant." [/highlight]
55cid 7.5:1 Compression, hemi-spherical style heads, 90 degree valve angle, 4 cams
Production Information:
XL (1983 units), $1,103
1958:
XLH introduced with higher compression and larger valves
Camshaft gears became integrated with the camshafts, eliminating the need for a woodruff key.
Drive gearshaft was enlarged .125 in.
Drive gear and second gear support shaft was enlarged .125 in and had 8 splines (instead of 6).
Choke control lever moved from left side to the air cleaner.
Heavier clutch cover and new gasket.
New oil resistant clutch hub seal and gearshaft o-ring.
Two brush generator.
Optional turn signals and 1 in over suspension.
The XLC & XLCH (Competition/California Hot)
Larger ports and valves
High domed pistons
Light ended tappets
Magneto ignition
Production Information:
XL (579), $1,155
XLH (711)
XLC
XLCH (239)