I'll weigh in too as a LH flint shooter for 50 years. My first rifle was a DGW Numrich Minuteman rifle- piece of junk! RH was all that was available. Built my first rifle in 1985- RH, due to a good kit deal on $ from mentor Vaughn Goodwin (previous NMLRA Pres). So, shot RH guns left handed for 30+ years. Only problem was RH cast off which slapped my face. Never had issues with the lock on same side as my face, or any loading / priming problems. Now I build all my long guns LH, mostly using LH Siler locks. There are LH kits available from Chambers, TVM, and Pecatonica. Pre-Covid, TOW had some, but presently no offerings. While limited, there are LH options for kit builders, and beyond that, one can go the profiled butt option on a blank from folks like Dave Keck at Knob Mtn, who will do LH offset. I won many matches shooting my RH guns left handed. If the gun fits- RH is fine. Just watch the offset. I get quite a few comments about those "backwards guns", but if you don't try, you'll never know how well you can do with a perceived shortcoming that is probably not significant. Sure is nice to have a cheek piece on the preferred side, without PB screws digging into your face! So, no fear about shooting an opposite hand gun as long as it doesn't bruise up your face. At least on a kit you can remove more wood if needed due to cast on if it's not too much. So try it before you let bias win! We lefties have had to adopt to a RH world all our lives. I remember doing the M-16 Hoochie-couchie "the shell goes down your shirt" dance
and adapted by buttoning the collar button. We can overcome!