if ya look at the link powertroke444e noted from ebay. and enlarge the pictures.
you can make out 2 guide rails. that hold the sickle bar up off the ground. and allows the bar to follow the ground.
one right at the base of the bar. then a smaller one at the very end of the bar. ya let the bar down. and the rails hold the bar up off the ground. the ones i have seen. you can adjust these guide rails up and down to get different cut heights for example 1" to 4" cut heights. (well maybe not that big of difference but hopefully get idea across)
went to auction was it last week. and saw some sickle bars, i wanted the trailer / pull version. that ran off of the PTO. with a single hydrualic to lift bar. but it ended up going way over, what i could spend. and ended up getting a 5 foot bush hog pull type for $55 bucks.
the trailer pull type looked like the ebay link, but was i would say in worse shape than what ebay one looks like.
i would of went with the 3pt hitch types, but the old allis chalmers CA tractor has snap coupler setup vs a 3pt hitch. and spending 400 plus for 3pt conversion just not worth it now for me.