Matt, if you're talking the current Ruger guns then the .448 pilot is probably perfect.
Without a pilot I would not try to use a reamer. Too much chance of screwing it up. So just see how the .448 pilot fits before you try anything.
Yes you can shim a pilot but tape is usually way too thick, probably 0.004" on average, maybe more.
Go slow, use plenty of cutting oil. Only you can judge whether your mechanical abilities are up to this task. It is not really too different from tapping a hole for threads, so if you can do that, you can probably do the cylinder.
I myself like to do such things but also recognize that I could screw it up and am willing to pay the cost to have someone else fix it, if necessary.
Let us know how it turns out.