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Whew, I knew I should have looked in earlier!
As Mike said, the 'Autumn' guitar on my web site(under 'New Work') is a 12-fret 000 with X bracing. I also built another about 4 years ago. Both used BRW for the back and sides, but the first one had a Red spruce top. When I finished it up I thought 'I'd like to hear that same guitar with cedar', so...
This is not such a 'weird' project. The 12-fret 000 was the last and largest guitar Martin designed for gut strings. The fact that X bracing proved strong enough that you could put steel strings on those fairly large boxes does not mean it won't work with nylon strings. However....
X bracing gives you a higher cross grain stiffness in the top than fan bracing does. One effect of this is to move the 'cross dipole' resonance mode of the top up in frequency. For reasons I don't want to go into at the moment (time) this seems to have the effect of increasing the mid-range output of the guitar. The sound is a bit more 'solid' and the mid-treble balance is different from that of a fan braced box.
The effect is exacerbated by the long 000 body, which is about an inch longer than most Classicals, and wider too. Longer bodies, all in all, tend to be more 'bass balanced'.
All this can give you that real deep 'Spanish' sound, but you have to be careful to get the trebles to come out well to balance all that bass. You're off to a good start with an Englemann top, which should be both stiff and light. I thought the Red top I used on the first one was maybe a bit too 'forward' at first, although I did not get a chance to hear it play in. The cedar top on the 'Autumn' instrument works well.
That guitar has a 'double X' braced top, with the X crossings at 90 degrees. You might want ot change that depending on the cross grain stiffness of your top. That top is a cose-grained and fine piece of cedar, and it's 2.7mm thick from the top edge to the bridge, and tapers down from there to about 1.8 at the tailblock. The bracing is Red spruce 1/4" wide, and it's 11.5mm high at the main X crossing, 9.5 high at the bridge line, 8.5 high between the bridge and the X, and tapers off from the high point at the bridge line to 1mm high at the bottom end. The upper end, above the main X crossing, tapers pretty smoothly to 5mm high at the inlet. The lower X is 1.5mm high where it goes under the main X at the bridge saddle line, 4.5 mm high at it's crossing, and tapers to nothing before it reaches the liners. I used a thin spruce bridge plate, even though I used a tie bridge. What the heck: nobody is logical all the time. The upper cross brace is 13mm high. There are two 'A-braces'7mm squre that go from the upper arms of the main X past the soundhole and _through_ the upper cross brace to inlet into the neck block. I hate when the neck shifts.... Top weight before gluing was 172.5 grams. I did not note the bidge weight, but suspect it is about 24 grams.
The rest of the guitar is pretty 'normal' except for the decoration.
The tone is, as I say, pretty deep, although there's enough treble and clarity to keep it from being 'tubby'. You can hear me attempting to play it on 'The Carol of the Birds' on my site (also under 'New Work': we gotta do something about that), but that may not tell you much. Aside from my playing I used my RadShack dB meter for a mic and recorded it on my computer through the Sound Blaster AWE32 card, so it's not exactly 'state of the art'.
If you wanted more treble you could substitute spruce (which you are doing), and taper the top in the wings of the lower bout, leaving it thick at the tailblock. A lighter Indian rosewood bridge might help, too. I can't say how it would work with scalloped braces.
Hope this helps.
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FAQ
If I stay with x-bracing I figured I could narrow and shorten them by about 1/3 but I still think the bass would be over predominate. I think if I could keep the cost down that I could build a good student guitar from this method. That is one market potential I have not tapped around here. I hate to work with laminates but have more than just a few inquiries the last two years for moderate priced classicals. With all of my experience being in steel sting, in the past I have shyed away from these inquiries.
