I've never tried a Blue in a Fender blackface amp. I understand they're good in tweed twins. I wouldn't dare try one in my 6g3 -- I'd be afraid I'd blow a $300 speaker.
For blackface amps, I generally want a ceramic speaker like they came with. Weber 12F150 is my favorite, and what I have in my Deluxe Reverb. It's significantly cheaper than any Alnico speaker, especially an Alnico Blue.
Did you stack the Weber 12F150W against them? Probably you'd get one for even less than the Emi and who knows: even more exuberated by it - or not. Certainly has more texture and cone to it per the original Jensen.
From certain PoV I can see where you're coming from, the mid '60s style american being perhaps the most british they ever where. And yeah: you don't have to have alnico as long as the response is smooth in itself.