magnum head conversion pushrods

Hi, I'm searching for pushrods for magnum style heads on la block, cam is hydraulic flat tappet, I've read that boss 302 pushrods work but I found that they have differente lenghts from 69 to 71, so I wanted to know what pushrods lenghts people are using on this kinda of combo I was looking for Comp 7492 ones, should this ones work? I know that the correct way should be measuring my engine but I can't do that...