KZ650 Frame question

I want to buy a kz650 for the purpose of doing a 70's custom using, among other things, a Tracy body. Since the Tracy's are model specific, my question is about the various years and models of the 650. Were the frames changed for the SR? Or changed over the years like the 900/1000 were? My Tracy will fit a Standard 76 for sure. The 78 SR comes better equipped for my needs, but I can't be sure it works till I buy it and try it. I don't want to have to alter the body. thanks

ps- I don't want to go later than 79

I'm pretty sure the sr frame is different.

Mark

B&C frames are more or less the same, D (SR) are different, mainly at the back end loop of the frame.
Later E&H frames are different again, with more bend to lower the seat area.
F frames should be very simialr to B&C.