I have a pair of cased Boswell, Best BLEs 12ga with side levers on the right. These guns have been traded around the Carolina Vintagers for 20+ years after coming to Charlotte from the old Cape Outfitters.

We didn't have access to the Boswell records until years later when Chris Batha confirmed their provenance. I waited nearly 20 years to become the 4th owner of this pair within our club.

They are the only pair of BLE side levers I've seen. They are also the only side lever Boswells of any configuration that I've seen.

When the Boswells first showed up in the US, the early Internet listings were text. The pair was dirty and looking worn. GunsInternational, et al had not appeared.

Over the decades the pair were re-browned, properly cleaned and re-oiled. I am thinking of an article for the DGJ. The guns really have a great story to tell. I'll co-author with Matt Haney of the Georgia Vintagers.

I haven't posted photos on the BBS in years. I'll get some photos online so you can see them.

To the question of right side or left side, I am firmly right side for a right handed LOADER. I have used these guns as a pair in flurry shooting both as shooter and loader. A gentleman of the era would have used a loader on the grouse moors. When loading, the loader gets a fired gun, moves it to his right hip and opens the gun. With the gun tilted properly, the loader only has to drop his hand a few inches into the shell bag to expedite a quick reload. The right side lever makes this very fast with minimum motion.

I have loaded for the Vintage Cup Flurry events for many years. The only configuration that I found faster to load was a pair of SLE top lever, self-openers. (Probably why they won out in the market place)
Typically for a 4 minute flurry, I can load:

Top lever pair, 75-80 rds
Side lever pair 80-90 rds
Self-opener pair, 90-100 rds

I always start a Flurry event with 100 shells. We count the unfired shells and compare with the score. The best I loaded was 98 shots. I was down to my last 2 rds when the whistle blew.

Joe in Charlotte