They are machined as a pair when manufactured. I think you might be able to use mismatched cases but I would be very cautious when doing so. Assemble and make sure everything fits nicely, then slowly tightened things down as a dry fit while making sure everything rotates freely until completely secured and torqued.
I would recommend a matched set, but if you have to use a mis matched set, this is how I would proceed.
Sent from my iPhone using Tapatalk