First off, welcome to the forum! Be sure to check the newbie thread for forum tips and how-tos.
Second, I want to point you to this piece by Tom Woods.
Next, it would be helpful if you were to check out the resources he cites, in particular The PIG to the Great Depression and the New Deal and the Keynesian Predictions vs. American History lecture.
First it needs to be recognized that much of his conjectures are non sequitur or correlation/causation fallacy. (e.g. his whole section regarding Murphy and the GD. It seems that he is asserting that just because high unemployment followed deflation, it was therefore caused by it. Same thing when he says “if there was ‘pent up demand’ […] we should see that inflation skyrocketed before and as private output increased in 1946.”) Next, for data on this, you might check chapter 5 of Meltdown, in which Tom Woods briefly discusses some of this data he relies on, such as GDP.
Further, for Keynesianism in general, there are so many resources on this there’s virtually no debate to be had that hasn’t been had before. See here: