I cannot answer definitively, but just to give you some hope I am pretty sure they are backwards compatible.

I have a 2010 X748 with 62” deck and would like to know for sure, too. The 62” deck is larger than I’d like, and I wonder about swapping for a 54”.

Someone will let us know soon.

P.S. Welcome to the forum, or congrats on post #2 anyway!

 

They are compatible but you have to keep two things in mind. They are as tall as a 7-iron deck so will not raise as high as the old deck. And the HC deck requires a different rear draft arm (not arms, it is one piece) about $200 I think.

I do not know if the older tractors can use the auto connect.


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Thanks makes me wonder if the deck not raising as high also applies to a new x700 series. Did they change the frame?

 

They added another hole further up where the lift arms connect to the frame if i remember correctly. Here is a link to the 7 iron brochure - if the HC deck is the same stamping as the 7 iron then it seems to reason that it should fit. 60-in. (152-cm) 7-Iron™ deep-deck mower delivers commercial capability

The main difference will be to swap the separate draft arms for the (double?) T style that is on the later model machines.

https://partscatalog.deere.com/jdrc/sidebyside/equipment/81532/referrer/navigation/pgId/606865298

Here's the sales brochure for the 60HC:

John Deere - Sign In

And the 54HC deck:

John Deere - Sign In

I believe that the max lift height is slightly lower on the 7 Iron and HC decks but i'm not positive of that - it might be that the cutting height is the same as the other decks but the shell hangs down a bit further than the other decks (hence the HC) making it seem like it doesn't lift as high.