Hi Robert,
Thinking about all this one more time, at this point it may be best to keep the 8 cu. ft. box since that volume IS correct and keeping the 45 hz tuning frequency also makes sense in the context of two possible driver Vas numbers (275 L. from JBL or 427.7 L./15.1 cu. ft. calculated by 4313B in a 2003 post about the purpose of the E-145). If JBL's number is right, you get a small bump in the lows to sort of "match" with driver rising mid response, therefore "balancing" the sound. If 4313B's number is right, you get flat bass response which you say is not a problem with your Driverack to adjust or equalize to again sort of "match" levels with the E-145 rising mid-bass response. Keeping things as is for now, you can get "the best of both worlds" as they say, or face either applicable scenario. Not a bad thing at all, and a great outcome in this dilemma.
As for the proper vent length issue in the new version of Win ISD, I'll install the software and check that, plus I'll also review my vent numbers in Winspeakers...
Will be back in the near future.
Richard