The B329 is a double triode with separate cathode connections. An amplification factor of 17 is quoted. The data-sheet makes the point that Type B329 is the commercial equivalent of CV491.
The each triode section can dissipate 2.5 Watts.
The working part of the anode is about half the total width, the rest is cooling fin.
The thin glass tube envelope is 20 mm in diameter and the length excluding the B9A base pins, is 49 mm.
References: Datasheet & 1040.