Hi Mark,
I believe you recently bought this car from ebay, from seller bcrt...correct? I, and our club historian helped advise him as to what he actually had, some of the history, etc. on this car. There's a thread in the "Cars For Sale and Wanted" section where you'll see it posted (I'd linked to the Ebay sale, in case any of our members were interested), along with the info our historian, Jack, helped provide.
As to a new windshield, we have a club manufacturing fund that produces some parts no longer available, and they have new '51 windshields in either clear, tinted or tinted and shaded glass, $425. However, to gain access to to the fund you will need to join the club, which is well worth the money for just the quarterlies and monthly newsletters alone. There is a one time $10 donation to the manufacturing fund on your first order, after that just the cost for what parts they do reproduce. There are several levels of membership...I can highly recommend the $25 per year level which gets you digital copies of all newsletters and quarterlies, along with access to the manufacturing fund of course.
On windshield gasket I'm not sure, though it's possible Larry Barker may still have some new/old stock on that. Larry has many nos and used parts, as well as several dozen cars in varying stages of condition. He's a great guy and is a font of info on these cars. He lives in Arizona and can be reached at 480-843-8110. There is also Willow Run KF Parts, who may possibly have the gaskets...kfparts.com.
Also, I too have a 51 Deluxe, though a 2 door model, and have asked many questions regarding it over the last year or so. If you do a search on my nick you'll find much good info on this particular model through questions I've already asked, and a search on 51 Deluxe through the forum will turn up much more.
Welcome to a dedicated group of KF owners and enthusiasts! We're more than happy to help in any way we can.
Barbara, would you be so kind as to send Mark a digital sample copy of one or two of the newsletters and or quarterlies, so he knows how wonderful they are? Many thanks ma'am!