The PT2399 works just fine in this application. I've already done it. There are existing boards out there that only require +12VDC which you can easily tap off the filter cap on the S&T board.

ebay.com link: Synthrotek PT2399 Delay Dev Board PCB Printed Circuit Board only

I did this while I was "experimenting" too and it worked fine. In fact, its an easy and cheap way to add echo to non-Centaur S&T games. But its a bit messy wire-wise.

If you really want to offer up the design to the Pinball community you could do the PCB on OSHPark. I believe you can make the design public and anyone that wants to can re-order with future runs.

https://oshpark.com/

Very Nice! Exactly what I was planning to do with the PT IC. Yours appears to use the Holtek IC. Do you have plans to sell any blank boards? I would be interested in some since I have about 5 8955's and ram in stock.

While changing the B to a P probably works, you probably should have left the zooming ball Logo off. I know you slightly altered it, but it is still awfully close to the original and would probably fail any legal battle.