Would Vanguard still be built in this timeline?

Would HMS Vanguard be operational by 1942, and would she still look like the historical Vanguard?

Probably: the existing plan to use spare 15-inch turrets still makes Vanguard a distinct and useful design.

Vanguard would probably still resemble the historical ship because the design already existed as a way to use spare 15-inch turrets. She was not simply a late substitute for the King George V or Lion classes. In this counterfactual, the King George V class replaces the R class while the Lions eventually replace the Queen Elizabeth class. Wartime priority could bring Vanguard into service sooner, but her distinct design rationale remains intact.