I would never say never on the backfire, but can't imagine how that could occur, but again never say never. I personally hate start retards they seem to cause more issues than they solve. With a separate start and ignition circuit, like 99% of racecars have I have never seen the need for them. I would lean more toward a defect in the oil pump shaft itself, that shaft sure does not look like it was "twisted" off at all. Curious what weight oil and ambient temp?? Maybe a slight alignment problem, I have seen it before and on a older version of a World block......But you would likely notice that on install.