So confused - waste valves.

[Spookies]

Hello everyone,

I am so confused about my current waste valves and flanges. Nobody really could help me from trailer companies that I sent pictures. This is 72 Tradewind. I want to change all parts with Valterra but some says I can't because of my black tank has a older fitting. If I can which parts do I exactly need? And also I am confused about the sizes (there are 1-1/2" 2" or 3"). I appreciate your help. Please see my current one.

[68Streamline]

Vintage trailer supply sells this plate/adapter.
http://www.vintagetrailersupply.com/...-p/vts-954.htm