With a cap upgrade, numerous posted tweaks to a simple 1st order xover, the original - darn good 8" woofers, i would just spend the maybe, $100 and grab a used pair. You can upgrade with the new tweets (recommended Seas and Morel tweeters for about $50 [try Madisound] and some basic xover modification (you can bypass the tweeter attenuation pot altogether if you like, plus a few other tweaks) you would get some nice high frequency extension. Check out all the posts at both Vintage & Speaker forums on Audio Asylum for more info -- it has been discussed many times over there.They were so popular that you are bound to find a local pair in nice shape on eBay within, say 3 months and you won't have to worry about shipping.
But hey, i'm a vintage head -- to me there is some voodoo magic with what makes the Dyna A25s sound so natural.. they had no business sounding as good as they did back in their day - they'd sound even better with a slightly increased enclosure size (that would be a really worthwhile project, using the original drivers, with maybe just a twweter replacement and building new cabs).
Seas makes great drivers.. so they may sound great -- i just wonder if they'll improve upon the old magic and the orig. with the new tweeters sounds brilliant (i run some in my office system).