Take a look at the
2123 data. They show the response in a .25 cubic foot sealed box. Low end starts dropping gracefully at 300Hz, and is 10dB down at 80Hz. HF goes out to 5KHz, and drops like a rock. Highest recommended use is to 3Khz. The 10" cones get pretty "beamy" above that freqency. The term "brain dart" comes to mind.
I see no problem using the 2x10's right on top of the C-V's, at the same 150Hz crossover point. Run them up to about 2Khz or so.
The 2410 is rated at 30 watts when crossed over at 800Hz. Starting them at 2Khz should improve power handling considerably. Run these up to 6Khz, as that's a nice point to bring in the 2405's.
I have used 2405's from 6Khz up, but it was over a 2482, which is a 2" mid driver rated from 300Hz to 8Khz, IIRC. FWIW, I really love(d) the old JBL Slotz. How sweet they were.
In my experience, this should be a good sounding system. The biggest issue in losing the HD15 cabs is probably stack height. You need something to get the HF up in the air, like say an amp rack or road case or something.
Ahhh...the good old days!
Ballpark figure for a modern 2-box per side, active 2-way rig (I'd recommend a pair each of EAW LA325 and LA400) and the power to drive it (all the amps you have are too small for this kind of thing) would be about $8K.
Spending less would give less performance, but offer higher portability.
If you can tweak out good sound from a rig like the one you descibe, a 4-box EAW LA rig would be childs play. The stuff you have was pretty dreamy in it's day, but I doubt it has much resale value in todays market.
For shits & giggles, I'd just get some Crown PSA2's, BGW 750's and Blaze...I mean Phase Linear 700's and make it a true "period piece". ...Don't forget the 2-pole Hubbell twist-locks. Recessed males in the amp rack panels and speaker cabinets, and females on BOTH ENDS of the speaker cables.
Stop me! I am just being silly now!
Ahh...the good old days