According to his wikipedia page, he claims that he found the use of LSD mind opening, that he believes it helped him come up with the idea for PCR, and that he doubts he would have come up with it if he never used LSD, but it doesn't say that he came up with it while on LSD, and I would take it as implied that he did not. This does shift my prior in favor of LSD having been useful to him in developing PCR, but not a whole lot, because there's such an abundance of evidence for people having poor self assessment regarding the propensity of drugs to aid their thinking. Even a non-blinded experiment which compared some measure of intellectual productivity of an experiment group on drugs to a control group that wasn't would do a lot more to change my assessment (and it is awfully hard to adequately blind subjects to whether or not they're taking real hallucinogens.)

Do you have a source for that? I remember reading in his book that the idea came to him in a flash while he was driving on the freeway. It could be my memory of what he wrote is mistaken, or he's just that kind of crazy guy, but driving on the freeway implies not tripping on LSD.