actually i've just sold off all my SU stuff, I had a pair of HS4's ready to rebuild and bolt on just for the hell of it- until I realised i just wasnt going to get time. never done it myself but have read up on them, but they seem easy enough to tune
I cant see why bolting another hitachi on wouldnt work, unless they are difficult to re-jet. you'd need two downdraught 2-into-1 fannymoulds though, could be tricky with all the crap hanging off the side of em.
if you wanna give it a try give me a shout, i've a whole plethora of K10 carbs and manifold in my garage, crying out for a good home!