Here is what I would recommend, based on the .54 barrel I had Ed Rayle make me back in 1988...

I went with a 1-72 twist although I believe a 1-66 would be fine...As to rifling, go with
.012-.014...A coned muzzle would be nice, back then I had never heard of one, I've thought of doing mine by hand but I figure if I have put up with it this long why change...