What capacitor values?

Well- That would bring your tweeter in a little above 10kHz, and your mid- right about 4kHz. The mid isn't doing much midding that way. I'd say 80uF on the mid(500Hz) and about 5.5uF on the tweeter(about 5kHz). I suppose if you were to go with an iron core inductor on the woofer, you wouldn't have as much insertion loss(though it may become non-linear at high input levels). If I were doing it, I would use either Solo or Alpha-Core air core inductors(very low insertion loss and phase shift, very transparent). The value of the coil would depend on the impedance of course(8ohm=2.5mH, 4ohm=1.27mH for 500Hz). I suppose a .13mH to roll off the mid at 5kHz wouldn't hurt either. You may find yourself having to pad the tweet and/or mid to match their outputs with the woofer.

Thanks again Rodman.
Whilst the formulae indicate that with the 10uF on the Mid it should only come in at 2000Hz, it patently doesn't.
The speakers have always sounded effortlessly brilliant as all my audiophile friends agree.
I don't want to mess with that distinctive balance and by inserting new Dueland VSF caps for the existing cheap 30 year old ones, I hope to hear improvements.
The Scanspeak tweeter comes on song at 1500Hz so I don't understand your thoughts on pushing it up to 5KHz?
I thought if I left the tweeter at 2.2uF and increased the Mid/Woofer to 40uF (compared to the 10uF it's had for 30 years?......it might improve the overall sound without affecting the character that I love?
What are your thoughts on that?

If you like the sound: Leave it as is! You've no one to please but yourself. Based on the impedances you gave, the values/points/slopes should be as noted. I was suggesting what generally works well for x-over points. Especially with a 12"/5 1/4"/and tweeter. Happy experimenting/listening!

One final question Rodman,
If I change the cap value on the Mid/Woofer from 10uF to 40uF, what is the possible risk/downside as your best guess?

Mr H- No risk at all. It would bring the mid in at about 1kHz which is probably closer to the the neighborhood of the 12's natural roll-off. See if you can find the data on your 12". Often that will supply you with a freq response plot. Check it's 3db down point(upper) and design accordingly, if you don't want to use an inductor.