A.) I would NOT re-line and chamber in 25-20 W UNTIL I had a good pile of raw brass in stock. EXCELLENT choice in chambering, just calling out potential availability issues.
B.) With a fast (NOT pistol appropo) twist liner, and 210 gr cast .357 bullets, you just might want to look at the .38 spl., shortened up to .38 S&W,...that action does not like really long cartridges, never has.
C.) it's not a "lever action".
D.) for a FIRE STORM of good opinionating, move this post over to the Single shot and BPCR forums.
.......if you're not baffled by brilliance, I guarantee you'll be baffled by BS.
Congrats on having a nice piece of raw material,....just keep in mind what Frank DeHass said,...single shot smithing is not "entry level".
GTC