Wait, the 24" varmint barrel is not just a longer version of the 20" bull barrel that comes stock on the 457 Varmint model? I'm pretty new to this whole CZ thing, so I was under the impression that the 16.5", 20.5", and 24" varmint barrels were all just varying in length, not circumference. If it is narrower, that could be an option for me.
Regardless, I assume the 20" bull barrel should fit fine in the synthetic stock, since that is what the CZ website is advertising now (they say the synthetic stock will handle any barrel without configuration)