First and foremost, WELCOME to the Forum! You will find a lot of great advice and how-to here. And we will be more than willing to help you climb that learning curve. We've all been there, done that (BTDT)!
Second, congratulations on having your 90 year old father help you with all of this! That is extremely impressive! (I wish my Dad was still around to help me!)
Third, it looks like you have a great start to the layout. Congratulations on identifying a space for a layout. That's always a tough one. I do have a question for you on it though. Give or take a bit, where are you located geographically? How hot or cold does it get in the attic? If either are major extremes, you may want to consider insulation and some lighting before you go much further. Unless this is a temporary setup and you are moving the layout elsewhere in the near future. I know summers and winters in the northeast can be really rough when you are in an uninsulated attic. (Don't ask me how I know this...) 
Fourth, to answer your question, on the ZW there is are 2 rings, one between the A handle and the B handle, the other between the C handle and the D handle. One each are a pair of black and a red marks. With all 4 handles down (no voltage) look where the zero marks are on each side. One will line up with the red, and the other with the black. Lets say the A handle line zero lines up with the red mark (could be the other way around). The B will line up with the black. Same thing on the other side. When you cross from one circuit to the other, just match the marks for the A and D handles. You might be off a bit, but you will be close enough not to have an issue. You will need insulating pins on the center rails of the crossovers. Whatever you do, DO NOT pull the insulating pins from the common rails of the switches! Those are needed to operate the non-derailing function of the switches. Depending on exactly what you want to do with train operation, a SPDT may or may not be necessary.
Fifth, what can you tell us about the green AA Alco diesels?
Chris
LVHR
