We've mostly been figuring a 10" high box. If you port through the top, it has approx. 10" on the inside, but space is also taken up by the horn. Using a 10" box on the bottom will be fine.
'86 LaScalas (LS-BLS w/s) w/APT150 tweeters and DHA2 crossovers, '89 Heresy IIs, '72 JBL 4311s, JMA Merlin Pre, Welborne Labs 2A3 Moondogs, Former Dynaco ST-70, H/K 430 x 2