I've compiled a .pdf comprised of a complete set of mid-1970's JBL enclosure plans from my files. JBL mailed these to me when I was building cabinets, and inquired about specs, oh-so-long-ago.
NB: These are NOT plans for cabinets JBL sold - they are plans for fitting JBL transducers into non commercially available designs. So, don't get your hopes up that you'll find any thing even resembling a 43xx series cabinet, or whatnot.
The plans have numerous cabinet and baffle configurations, with cut-out dimensions for most LE-series ("Home) transducers and K-series ("Musical Instrument") elements. In addition, there are "JBL Enclosure Porting Charts" guidlines for both the "Home" and "Musical" series.
I had uploaded these to the JBL Heritage site but they've not made it to the limelight. The format may not work there.
If anyone has interest, please pm me with your email address - I'd be happy to forward the file. The file is 1,033 kBytes.
Here's an example: