I'm not familiar with those, I mainly sell/use the 8 port versions of 5 gallon tanks.. it does look like the Firestone tanks that are a little slimmer though.. in that case, it'd be about 34" long.
I have the dimensions of the tanks I sell posted beside them on my site, sometimes you can just assume the size is close by looking at pics since 5 Gallons are usually in the same area in size, except some are short/fat, some long/slim.. maybe these can help:
http://whynotfab.com/store_tanks.shtml
You could always try calling streetbeat or ART also. Good luck,