I have many years experiance rebuilding Velvet Drive, Paragon, Hurth and ZF transmissions. I will attempt to answer your questions about maintaining your unit or about how it works.
I do not recommend prop sizes leaving that to the prop people!
I have two (2) ZF220-IV 1.772:1 electric shift control V-Drive transmissions for sale. These were trade-ins and porported to be running removals although I cannot verify this. They do not appear to have had any water in them.
For sale as used units only, as is, no warranty. $500 each
Call...