Wow, really nice!! You beat me to it. Good job!!
I like the M2 style fronts & paint and the "integrated" ports. I did the original port version but yours are better looking. Similar bracing. Really stylish! A keeper for sure.
Please give us some feedback when you have had the time to listen and measure. Interesting to get some info on how you like the lower vertical dispersion compared to the M2's. Less floor and ceiling reflexes shout make a difference albeit very much up to the room. Very exciting!
I made some low stands for mine, but maybe they are not needed.
I think I have stickers for the horns if you like. Without the holes for the pot's. 4367M for "Modificata" :-).
I also have soft vibration dampening feet if you need. They are stiff vertically and soft horizontally which implies that they absorb vibrations without being soggy. I use them on all my big speakers (especially subs). About 50mm dia and 50mm high. Mount is a M10 thread at the top. I typically bolt mine from inside. Same technology they use to stabilize helicopter dash's. You can sit on the speaker with no problem but you can push them sideways with one finger. Magic stuff.
Wool felt in combination with some kind of "fluffy stuff" is a great combination to reduce back side reflexions behind the woofer. I bet those will show very limited cabinet vibrations, which should correspond to clear midrange. Excellent.
I will also use 2451SL's like you. I'm just in the works of building a nice matched pair.
I think the 2450SL/2451SL does have a "calm" in the sound that differs from the D2's. I do have a set of D2's here also. Maybe just a matter of taste as the D2's do measures brilliantly in these and the M2's.
You can XO at a lower frequency with the 4" compared to the D2, as the 4367 wave guide loads the 4" driver lower compared to the M2.
I have a full set of measurements if of interest. 9 different JBL 1,5" drivers on VTX, M2 and 4367 wave guides @ 90, 60 and 30 degrees, short and long windows with graphs and data files available. About 400 different measures.
I will be running mine active with DSP and I'd be happy to share the settings, once done.
Now, get a whiskey, a comfy seat and enjoy your creation :-)