Hi Mike
Good news
Dimensions of my rack between post centres are:-
Front to back centres 355mm
Width centres 385mm
But please check yours, when it arrives. These dimensions are governed by the hole centres in the top and bottom shelves.

If you place your TT on the top you will need some decent mounts/supports (3 is best) to enable it to clear the octagonal tops as shown in your picture.
If you need to add shelves you will need additional shelf supports, which just push into holes in posts.

Hector

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