That's why

Yates was commenting on the white bolts, seems he had just finished a race engine for Yarborough's car and then got the news about the white bolts, which were in that engine- but they were not allowed to go back into a completed engine to change anything, so he had to build another complete engine from scratch at the last minute with the better bolts. Just shows the level of detail they go through, and the budgets they get to play with