the answer is very little
3 1/2 long 2 high and a inch deep
the 3 1/2 is the tube length and it is a two pass system the dwg shows the plates screwed with csk screws to the casting and the end casting bolted through into the casting , but there is no indiction as to the method of sealing.
in full size turbine condensers ( this is a triple expansion engine ) they are expanded into the steel TP and are made of brass tube
these are 1/4 copper in 1/16 TP
as there will be a vacuum out side the tubes and a small water pressure outside , so the seal would have to stand about 10 psi
Stuart