Hey, I just got a 70's super sensitive too. You need to be VERY careful when buying used ones, there were some years, I think 72-74 when some of the snare wires were differnt on the SS's and the drum would not tune up right because the snare bed needed to be cut differnt.
ALL super sensitives need a specific Ludwig bottom head to accomodate the extra long snare wires. I forget what the serial number of the head was, I have mine on order. I just bought the snare drum 2 weeks ago and I love it too!
If your going to get a 6.5 I would suggest getting a new one because the old 6.5's were kinda funky. I love my vintage drums, and I want a 6.5 too, but there were so many problems with that extra depth and with the snare beds that ive been scared into getting a new one.
And that dosent just come from my mouth, thats from Greg at Jacks Drum Shop, he is THE drum expert on vintage ludwigs, Jacks is the oldest operating drum store in the US! If your in the boston area check it out. I only shop there and they have been so good to me. If im ever short on cash I borrow money from the guys working there, and they are so great with custom orders through Ludwig Remo and Paiste (the only brands I play). I cant say enough about Jacks.