If I remember how my Remington c&b worked the lever was held up by a hook at the front but if you went with a hook you couldnt remove the cylinder. Not enough room to slide out the bbl pin with the cute short bbl. What if you moved the hook to the end of the cylinder pin so that the loading lever locked onto the pin? Depending on how loose the pin is a detent might be needed. Might be covering old ground. Nice job.
I haven't been on this forum for a few years and I find this little gem. Nice work. I've often thought about cutting one down similarly but without some of the cool touches you did.
Have you thought of simply tightening the loading lever pivot screw so it is tight enough to keep it from dropping but still will let you pull it down? I've set mine too tight and there's no way it would creep down under use.
Alternately, how about a screw to keep it in place? Early Colt SAA's had a cylinder pin retainer screw. Nothing wrong with that method but you'd need to have a screwdriver to reload if you wanted a drop-in conversion cylinder.