I've never done it, but seeing that your Dad's hands built it, that's enough "nostalgia-value" to me to have the barrel re-bored (if it really needs it) to possibly a .50 or .54 caliber bore to (I assume) retrieve the rifle's accuracy.
I'd never let that barrel get away... your Dad's hands, skills and heart touched everything on that rifle, including the barrel, and that's "enough" for me to keep it as he made it as much as possible with the exception of having it bored out to a larger caliber for accuracy's sake.
In this case, a reasonable amount of money spent to keep it as "original" as possible is no object, in my humble opinion, since the rifle is becoming a valuable and honored a family heirloom.
Jus' my 2˘.................
Strength and Honor...
Ron T.