You could contact somebody like Cliff LaBounty to rebore your .30/30 to .38/55. It would be a pretty straight forward process since the basic case is pretty much the same for both, same case-head size, overall length, etc. However, you couldn't rebore a .30/30 to .38/56 because the .38/56 shares the same case-head size as a .45/70, so the bolt face, tubular magazine, etc. would be all wrong.