fostex ff85k as a mid-hi in 2 way speaker

[mipop35]

Hi, my first post here.
I'm posting both in Loudspeakers and Full Range threads because I'm not shure wich can give more help.


BRIEF:
I will use a FF85K as a mid-tweeter with existing 10" woofer and box.
I'm looking for answers/experiences/suggestions in:

a) how to obtain the lowest crossover point in order to maintain the rated loudspeaker "program" power of 40W RMS

b) the smallest and easy to make enclosure for the ff85k at the above xover freq., since the original tweeter was a sealed unit.

FULL:
The original speakers are a pair of old JVC SK500II. Two ways, 50W RMS nominal power. Tweeter was 3" paper cone, but crossed well over 1khz I guess. Woofer an cabinet are in good shape. They will be mated with JVC AX2 Amp, 40W RMS, The same age and in total original condition.

FF85K fits almost perfect in the front cutout, but there is no enclosure for it because the original tweeter was a sealed unit. So special care must be taken in order to minimize the extra volume that will be extracted from the original speaker cabinet, since the woofer will stay the same.

I would like to set the crossover at about 500hz. I wolud like to know what power handling may I expect from the complete loudspeaker (or from the ff85k) at this crossover frequency. I remember I saw, in the distant past, some typical "music programs" energy vs. freq. distribution plots, but I can't find them anymore.

On the other hand, concerning the enclosure, the small volume requirements will almost sure push the resonance freq. of the ff85k/enc. near 500hz posing potential problems in the freq. response at the xover area.
I would like to know if someone has experience with the ff85k in small enclosures at 500hz. Could a vented enclosure help to get a smaller volume? Any "special" kind of port?

Thanks,
Diego