If JD combines/gps you can use "LAT/LONG +Heading". Have one machine set the line, and radio the lat/long co-ordinates + heading to the other machine. Then make sure they are set to the same width, and DON'T "shift the line".... ever.
We just use the heading and the second combine then just sets "a" when lined up properly to the first cut. With 1' overlap, it is quite easy to set up. I've found the 1' makes headland acquisition quite a bit more forgiving.
Setting up properly saves so much time by reducing wedges and strips that used to have to be cleaned up.
Both combines acquire data for mapping that is combined once it is downloaded to your desktop.
If they are both mapping then when you upload the data the whole field will be mapped. We harvested on a place last year with 4 combines (all different owners) mapping and the data was all super imposed onto one map, like one combine had cut it. You must make sure that there yield monitors are roughly reading the same otherwise it will look one combine was a much better purchase than the other..
As for running them together, like the guys said punch in the same co-ordinates and you shouldn't have a problem. So far as cutting a field out, if you go up and back, send them cutting from a middle point in each direction (ie east west) and when it is too far apart cut another land and start the process over again. If you go round and round, just set them off following each other.
Yes they will both be JD gps (GS2) . Only using SF1 though so not shifting the line through out the day will be a hard habit to break. I always open up the field with 2 or 3 rounds then cut up and back making a land be 10 passes wide. Also using 36ft 974 MacDon as they are Offset ( not centerd on the combine) so that makes it a little harder to be exact as well. Any more info will be great. Thanks for all the help so far!