[Shrewcub]

http://www.onlycubcadets.net/forum/s...ead.php?t=4633
According to this belt chart the 392 deck is for a LT. Without a picture of the deck you're looking at you will have to judge for yourself. The same chart shows that all GT 44" and 50" decks do take the same spindle belt respectively. PTO belt will vary by the tractor model.
In your first post you say the mounting seems to look the same as the rotted decks you have. Look at the 392 deck in the first link I posted. That clearly looks different to the 44c and 50c decks that I own. The spindle belt on the 392 is also different than the 44a or c. Maybe someone converted this 392 to work on a GT?

Edit: Welcome to OCC!