I would open both guns cylinder throats to accept 454 bullets.
If you shoot softer bullets with your lighter loads it will probably stop the leading, which is caused by powder gas blowing lube off the bullets where they are rattling. Using softer bullets allows them to slug up to seal off the gas blowby but also knocks the bullet out of balance.
The throats may or may not come out round, but don't be concerned abou it as long as the smallest dimension is larger the the bores largest point.
Most barrels are out of round, but they shoot fine.