Whoa, that is an impressive result, but more than I'm up for so long as the old speakers still work. If they should get damaged I might remount replacements to the door, but wow, that looks like a lot of work...

 

Just wondering if you've made any progress here?

Hopefully you aren't fixing this by trying to throw a new 8" speaker in there...

Was just thinking another option might be to review your current sub. You might find something smaller, like a nice SQ focused 10" sub in a professionally tuned enclosure might extend the upper range into the 150-ish region, rather than running out of puff around 100.
Realistically though, decent mids (your main door speakers), mounted solidly, should play down to 100. Sub's really aren't designed to play that high in the first place

 

Been preoccupied with non jag responsibilities, haven't addressed this yet - but it is quite noticeable and a disappointing in terms of audial expectations.