An interesting question Colin. Certainly, as you suggest, modern contras, at least in the U.S., are done with a walking step and often a buzz step swing, with some occasional improve moves(clogging, clapping, dips, and other forms of flourishes). In our region, a contra dance evening would consist primarily longways dances for as many as will, with some communities including squares, triplets, triads, four facing fours, and the like, with others having a zero tolerance for anything other than longways duple minors and four facing fours. At least here, if the call says, "Line up for a contra." the default would be to line up longways, with the ones crossed over.In our community, if the caller wanted some other formation, it would have to be specified as something different than a contra - "Find a partner for a square" , "Form 3-couple sets", etc. It's all about era and location I think...Here is a reconstruction of a contra dance published in 1801....I would not recommend attempting to call this at a modern contra....
https://www.youtube.com/watch?v=9F8hLaGFdZ4 Bob Green
St. Louis