Well, as I said earlier, not only could you fit the motor first (As you'd already realised), you could separate the dish and its backplate too.
Not only does that make the dish less cumbersome, but it will be easier to fit the dish bracket to the motor stub against the datum line and to ensure it doesn't go out of true as you tighten the clamp bolts.
Assuming the dish is going above the two Ks, then sling some polyprop over the upper T and haul the dish up that far. Then you've just got the final few feet to cope with plus a juggling act trying to screw the dish plate onto the backplate.
Unless, of course, you know someone with a MEWP?