[sdiy] cr-78 ram replacement

[J Brave]

Hi does anyone know how to determine which of the many variations of the 5101 ram chip would be the correct one? This is the one listed in the service manual: UPD5101C-E  

But I'm not finding that exact thing for sale - people are talking about replacing with Bally pinball ram - also 5051 on some forums, also there is a company selling an "equivalent" chip - but how do I know if I have the right matching chips? The pinball ram is far less pricy than the originals:

Pinball: https://www.ebay.com/itm/251898604630 
"Equivalent":  http://www.vetco.net/catalog/product_info.php?products_id=5199

Joel