A good point well made. I'll do you a deal, when I get 28 hours in a day, I'll buy a book on cabinet design and do this whole thing properly. ;-)
Looks like the Faital aren't readily available in the UK anyway. Its between the eminence at £30 or £70 and the B&C at £110. Just have to decide whether its worth the extra cost for the s**ty box it will go in.
The Faital is not an ordinary 8. It has a max displacement of 162cc, compared to 67cc for the Alpha 8. If your box is ported, the port will be sized for a speaker more like the Alpha, therefore undersized for the Faital. So the extra money for the Faital would be somewhat wasted (my point). If your box is sealed, same story, since the Faital isn't well-suited to a sealed cab. Moot for you if they're not available in the UK (that's surprising).
The B&C 8PS21 displaces 110cc; about the same as an Alpha 10. So again, the port (if it exists) would be undersized, but less so. The B&C also appears ill-suited to a sealed cab.
The 18 Sound 8MB400 would be another candidate (Vd 132cc). Ceramic, so should be less expensive, but again, you'd get the most out of it with a properly designed box.
If you're committed to that cabinet, you might as well get something cheap and readily available. Since you're in the UK, I checked Celestion, but didn't see anything better than the Alpha.