Ted, I may be able to help you a little bit.
First, make sure you have as many receipts as possible-the DMV wants to be sure they've collected all the appropriate taxes they can get from you. Do Not send in the originals-things get lost-send copies.
Second, anything you send to Harrisburg should not be mailed, but taken to your local state representative. They will/can deliver it to PennDot-and you will get your work back faster and with way less hassle than if a stressed out DMV employee gets one more envelope tossed on their pile.
Here is a basic fact sheet from PennDot on antique and classic plates:
http://www.dmv.state.pa.us/pdotforms/fact_sheets/fs-ant.pdf
You can use this to identify the next batch of forms you will need to see-most of them are available online-but your local AAA office is also a good resource for forms.
What you will need depends on if you want antique,classic,street rod or regular plates.In whatever case, you will need clear photos to submit taken from all four directions.
I haven't done what you need to do-but I did take a Model A with a old title, register it as a regular car and then change it all to a streetrod registration-I had to because of some modifications that had been made. Ultimately, my state rep was invaluable and the state vacated my old title and VIN and issued me a completely new title and VIN plate.
PM me if you have questions, or we could exchange phone #'s and talk. Good luck. Jeff