Differential cross sections for the reactions $^{10}\mathrm{B}(\ensuremath{\alpha},^{6}\mathrm{Li})^{8}\mathrm{Be}_{\mathrm{g}.\mathrm{s}.}$ and $^{10}\mathrm{B}(\ensuremath{\alpha},^{6}\mathrm{Li})^{8}\mathrm{Be}_{2.9}$ have been measured in the angular range from 9 to 25\ifmmode^\circ\else\textdegree\fi{} (lab system) in 1\ifmmode^\circ\else\textdegree\fi{} steps at ${E}_{\ensuremath{\alpha}}=46$ MeV. The shapes of the angular distributions are typical of a direct reaction, and the pickup processes are analyzed in distorted-wave approximations on the basis of an extreme cluster model, i.e., on the assumption that a deuteron is picked up from the target nucleus $^{10}\mathrm{B}$. Calculations using proper two-particle form factors are also performed, and the results agree with the former method. From the ratio of the experimental to the theoretical cross section, a relative spectroscopic factor ($^{8}\mathrm{Be}$-core-plus-deuteron-cluster parentage) is obtained and compared with two-particle fractional-parentage coefficients calculated in intermediate coupling.