You're welcome! Yes, rear panel removal to tweak sucks, so initially I used carriage bolts, wing-nuts and access panels, but due to cab weight and life long back issues, I finally switched to fixed/glued backs to increase cab rigidity and removable driver baffles a couple of years before Altec did on the 846B. Since the local distributor's in-house design team was aware of this and other tweaks I was doing............

Really, consumer cabs for the most part are just so-so furniture construction with mediocre audio performance, so consider either getting 'new' components and/or at least using what's in the Heathkit cabs and DIYing some cabs more appropriate for your new room's acoustics.

1 m measurements are fine for designing XOs and comparing different speakers, but this current obsession in the DIY community with billiard table flat responses at raw data to 24 dB/octave smoothing just because they can when no normal human can hear better than ~6 dB/octave resolution and will be much further away in an acoustically small room is not the best overall choice unless one sits at < 1m from the speakers in an acoustically large enough O.B. located outside on an open/flat field or similar.

Not familiar with Jim Smith's work, but unless it's very current and a thousand or two pages I suggest Googling for room acoustics websites and browsing the various DIY audio forums for DIYing room treatments to fill it out somewhat, though using horns with the proper polar response, speakers and listening position for the room, etc., treatments other than carpet or area rugs typically aren't required since LEDE rooms are best overall for horn and other 'focused' systems.

GM