Go with the extra barrels ......
Unless you need another receiver ......
As long as you go with a popular varmint round like the .223, .225-250 or .204 Ruger, etc. and don't modify them "much", they'll easily find second-hand homes.
As for the .45/70, along with the Buff Classic barrel, one or two other barrels are available too, or you could get a second BC barrel and get it shortened to whatever length you need.
That's how I plan to get a "heavier" .45/70 tube, but shorter than 32 inches. FWIW.