John, they are essentially the same machine, with the "Y" being the economy version.
That one was shipped mono and had no autospeed unit to play 33 rpm.
By the time I worked on these last tube Seeburgs in the 1980s the internal parts had been so swapped around that I wasn't even aware of the difference between the models as-built.
The bigger problem is this;
the wiring connectors are missing
Do you mean the plugs from the mechanism, keyboard and (ugh!) Tormat? This can be a significant hurdle.
I use selection receivers in my 201's and modded K from the original 201 type right through the DS receiver.
Speakers and speaker harness are NBD.
A stereo amp from a 222 on up through a DS can be made to work easily (one it is rebuilt). A transistorized amp from the LPC series is a good choice as well -especially if the speaker harness is missing.
Along with determining what is and isn't there (and what condition the units are in) you need to asses your own capabilities. Machines like this are often 'dumpers' where operators cannibalized good parts and later dumped in 'whatever" to make the unit at least appear somewhat complete.
I've built up machines from essentially just a cabinet and keyboard, but I had a large "parts pile" and a lot of patience.
Rob-NYC