Is there a list of the easiest to more difficult cnc lathes and mills to convert

pretty much the topic.
it seems like the bridgeport cnc retrofits are plenty and easy to do(probably due to lower cost and high availablity) But there are less documented cnc lathe conversions than mills. Not seeing many Okumas, or Hardinge lathes being converted. Any insights here? 

is there a list of manufacturers that use standardized serial and optical interfaces ? or which manufacturers that use proprietary serial and optical interfaces ?

Your question is backwards here. Every cnc machine is a bit different and there are literally thousands of brands. There is no "list" or "standard". You need to pick a specific machine available to you, and then determine what it has and see if linuxcnc can control it.

The only useful rule of thumb I can say is pre 1995 is most often analogue, and you can control it with linuxcnc. Post 1995 is most often some form of serial that you will not be able to make use of (unless it is VERY new and uses ethercat). But this is going to vary greatly, even within the same brand of machines and controls

Sure, I said "most often" and "vary greatly".

Take a break, eat some pizza, relax...

Wait, no, that's me. Mmmmmm piiiizaaa

haha

I was just pointed to a biesse cnc the other day form 1999. I am trying to figure out what drives they use. This is right around the time they transitioned from analogue to mechatrolink, and some of the LATER drives can support analogue and pulse as well, but older ones cant. A bit backwards to what you might guess on them.

The CNC world will be much nicer when industrial and hobby machines alike are on ethercat.... although we wont get any more $500 machines cause they wont go obsolete in the same way. Trade offs. haha.