TF 904 New Oil Pan Question

I just want to touch on a few bases here about the "Early" 904 that was used in your 63.
First you did the right thing looking at the the .org site as there is plenty of info there.
/6 Dan knows his stuff so read and go over the posts so you don't miss any thing.
Getting back to your 63, there is a mesh screen inside the pan where it picks up the fluid.Usually they are made out of brass and can be cleaned with brake clean or carb cleaner.
Your 63 904 has 2 pumps, a front and a rear so where the "screen" is you will see 2 holes(ports) that feed both pumps. The last year was 1965 for the 2 pumps.
Now you "can" replace this screen with the more common fiber type filter as long as it has 2 ports to pick up fluid for both pumps.They are still available at parts stores. I got mine at our local CarQuest.
You did say that you have the inline filter for yours so it will be up to you if you would want to change out the screen.
Your new pan will increase fluid by about 2 quarts.The spacer that is being talked about is to lower the pickup point of fluid in the deaper pan. It must have 2 ports to pick up fluid for both pumps.
I would call a Mopar specific transmission shop such as A&A or Cope Racing Transmissions for this spacer.(Google for their info)
In a nut shell you don't have to use the spacer and the transmission will work just fine with the fluid level at correct hight, you will just be gaining a few more quarts of fluid (more fluid,deep pan will help with cooling). For me,, I would install the spacer.
I hope this helps. Good luck with your 63,,,,I got one too !!