A quick look at the HNSA website comes up with this document for the Mk 9 ...
http://www.hnsa.org/doc/depthcharge9/part2.htm ... on page 15 are some dimensions depending on which Mod of the Mk 9 ...
Depth Charge Case Mark 9 has a maximum length of 27.625 inches and a maximum diameter of 17.640 inches. A support ring, 1/2-inch-diameter, is secured to the nose or forward end of the case by eight brackets. Eight fins are secured along the after end and are set at an angle of 20 degrees to the longitudinal axis of the case. The rotation of the case as it sinks is due to the fins and improves the underwater trajectory. A shroud or support band is fastened to the outer edges of these fins. When the depth charge is installed in a release track, its weight is carried by the support ring and shroud resting on the lower rails of the tracks.
Depth Charge Case Mark 9 Mod. 1 differs from the Depth Charge Case Mark 9 only in the details of construction. The case is of stamped shell construction which is welded circumferentially rather than the "orange peel" fabrication welded fore and aft. None of these changes has any effect on the handling, operation, or characteristics of the depth charge.
Depth Charge Case Mark 9 Mod. 2 differs from the Depth Charge Case Mark 9 chiefly in that the tail shroud is replaced by two rings and the angle of the fins to the longitudinal axis of the case has been reduced from 20' to 3'. The tail rings, the nose ring and nose ring supports have been made oval in cross section to reduce water resistance. The loading hole has been redesigned to facilitate loading the case. The nose of the depth charge case is weighted with 40 pounds of lead. These changes give the Depth Charge Mark 9 Mod. 2 a terminal sinking velocity considerably greater than that of the Depth Charges Mark 9 and Mark 9 Mod. 1.
Then on the webpage Part 2 with the second half of the document on pages 46 and 47 are some dimensions for the arbor that held the charge ...
http://www.hnsa.org/doc/depthcharge9/part2.htm ... looks like they were 28-in or 31-in long (tall when standing on a deck) depending on Mod used. It appears that the overall length of the weighted version is 3-in longer. If you are anal enough and want to scale out the different lengths ... go for it.

Otherwise roughly 28 or 31-in long and 18-in dia. is close enough.