I don't know the casting #'s, probably best to contact somebody like perogie ?
www.perogie.com for the numbers. I just looked for the off set of the carburetor to the driver's side, when I bought mine. On ebay I think they usually go for between $400 - 700 depending upon condition.
Supposidly, the advantage of the sidewinder is that it did have equal length runners, as opposed to other single four intakes which didn't.
Sidewinder intakes that have no wording on them have a solid plenum divider. The one's with SHELBY on them have a notched plenum, for a little higher rpm power. Ive only seen one with COBRA on it, and I can't remember any specifics about it if it differed from the other two. The runners are large, larger than the edelbrock performer, and performed rpm. The only intake that may be better is the blue thunder single four, with large runners.
With the turkey pan on, you can't read the writing in the intake, as mine is the SHELBY version. It's a great intake. Close to the best performance potential from a dual plane intake out there.