The latest "Conversations With Bill Kristol" interview is with Newt Gingrich and has some history of how Reagan became a supply-side tax-cutter:
GINGRICH: I was with Kemp before he went out to the ranch.
KRISTOL: Is that right?
GINGRICH: And Kemp said to me, "I'm going to go see Reagan. If he will agree to take up the tax cut, I'll agree to chair his campaign. If he won't take up the tax cut, I'm going to run."
More from Gingrich about Reagan:
if you read his farewell address, which is one of the best statements of his entire presidency – he says at one point, he said, "People said I gave great speeches but I actually gave speeches about great ideas." And I think it's one of the reasons why people like Clinton and Obama can't figure out the Reagan formula because you have to have the Reagan ideas in order to have the Reagan language in order to dance with the American people, who are, in fact, instinctively Reaganite.