Vintage FR BR ...adding a tweeter?

[waam68]

I have recently been experimenting with a couple of old 1940's/50's BR cabinets as I just built a "Get set Go" SET amp & wanted to see what SET/FR is all about. I don't have the skill to build horns & these came along free!
They aren't exactly the same cab design but are similar being about 4ft tall, 2 ft deep & 1 & 1/2 ft wide with a letterbox" type reflex port under the driver. One cab came with a vintage 12" FR "Grampian Reproducers" 15 ohm driver & I managed to score another driver off ebay very reasonably to make a stereo pair. Anyway swapped out the 1959 Wharfedale W3's for these & they are even more sensitive again, my 3W SET amp is driving them with ease. There is less Bass than the wharfedales but still a good level & the old FR cliche about realism on vocals & instruments on jazz/classical is definately there. The only thing they don't shine so well on is Rock as I think they are struggling to cover the top end & can sound a bit harsh on some recordings when pushed. The cabs are sealed with strips of material at the bottom & stuffed with really soft smelly wool & the walls are lined with 1" of wool felt mat (cabs don't resonate at all). They are Butt ugly but the sound is beguiling...anyway my knowledge of speakers is limited to reading Briggs "on sound reproduction" & "cabinet handbook" so standby for stupid questions....I have an old pair of Leak Sandwich speakers in the loft (original 2 way 15ohm ones)...If I wired the sandwich tweeters in paralell on top in a briggs style enclosure would this work or would I need a crossover? or is this just a bad idea?
Also anyone know if one of the Sandwich woofers could be turned into a kind of standalone subwoofer/bass helper (not necessarily needed but I like to experiment).
Mike
PS the bass on these is smooth