If you'll also be mapping the yields (I highly suggest this) then I'd steer clear of the 2600. Those Compact Flash cards are annoying and readers aren't real common anymore. 

2630 with AutoTrac would be a nice screen and TONS of them around. SF3000 for the roof is correct. There are two mounting "shroud" styles for the 3000. If the combine already has a mount on it (guessing it does) then you'll want to match that to the 3000 shroud type.