Bruce and All,
I had lunch with Al Ross today and I posed the question regarding the 596 boat. He sent me the attached photo of the 588 boat, at the factory. She and the 596 boat were built of the series of boats. It clearly shows that that series of boats did not have a windshield. Caveat: the 596 boat entered service in May 1945, and was out of service 12/45. While that is a very brief time, it does not preclude the possibility of a field fitted windshield having been fitted.
I hope this helps with your build.

@bruced I came across a Russian site that had photos which screen in front of helm.

Bruce,
My mistake, I misread your hull number. That said there is a nice head on view of 596 on NavSource. I would not say that it is definitive though. I can make out what appears to be a glass panel in front of the helm, but it could be reading into it as well. I have take a book down to Al Ross this week. I'll have him. He, of all people, should be able to answer your question.

https://www.navsource.net/archives/12/120559605.jpg

Very good detailed 4 view drawings

United States PT-Boats of World War2 by Frank D.Johnson does have a lot of pictures.
But not of that boat.
A few of the ones around that number do not have windscreens.
Canabus

@bruced
The one photo of her on NavSource does not appear to show a windshield. That said, it is a somewhat grainy photo.