I'd go for the different gun if you wanted to use conicals. In my eyes, the Blue Ridge .54 looks a little light weight with heavy charges. The Lyman Great Plains .54 seems like it might handle conicals better.
With the Blue Ridge, I'd use round ball. I don't know, but the thin wrist and short tangs might bother me some in the strength area. Just my 2 cent opinion.
I do like the way the Blue Ridge looks, I allways wanted the .45 flint. Very graceful looking rifle.