Lee/Grant Tractor

[Jakko Westerbeke]

Originally Posted by David Dunlop

what is it towing

That one is fairly easy: the barrel of a 240 mm howitzer M1:

Photo679697.jpg
(source)

To move it, this weapon was carried on two trailers, one with the barrel like here, and another with the mounting.

Originally Posted by David Dunlop

looks like a sizeable superstructure added to the outer sides of the rear deck

Those are standard stowage bins for an M31 tank recovery vehicle:

M31 TRV.jpg

(The bins are open here, they’re normally closed with lids.) The M33 prime mover is basically an M31 with its turret (which carried the crane) and much of the recovery equipment removed.