Vasicek's Model is the appropriate methodology to be associated with regulatory capital calculation under Basel II standards. It applies a one-factor Gaussian copula model to estimate the probability of default over a specified time horizon, making it suitable for Credit VaR calculations for regulatory requirements.

A is incorrect. A multifactor Gaussian copula model focusing on time-until-recovery is not typically associated with regulatory capital calculation for Credit VaR, as time-to-default is the primary concern.

C is incorrect. Credit Risk Plus does not use variance-covariance approaches; instead, it adopts procedures akin to insurance for calculating expected and unexpected losses from defaults, tailored for credit risk and not market fluctuations.

D is incorrect. Historical simulation for Credit VaR should involve the use of transition matrices and consider credit correlations, as these are critical for capturing the nature of credit risk.