Do you have any measuring/test equipment at all ?
A WT3 , or a signal generator, or even a CD with test tones of various low frequencies ?
If you have any of those, you can re-mount the woofers in their original cabinets and test them.
With the WT3 , just run a sweep , the low point in the woofers resonant peak is the frequency of the port tuning.
If you have a signal generator or test tones, adjust the frequency , going from low frequencies and gradually increasing until the woofer barely moves, then continue past until the woofer starts to move again. The point where the woofer is barely moving is the port tuning frequency.
If ball park is all you are looking for, measure the inside diameter of the tube , and the length from the inside edge to the outside edge. I would measure to the non-flared (longer length) edge. The flare on that setup is mostly cosmetic, although it will have some effect.
.......................Blake