by chuckthebeatertruck » Mon Jun 17, 2019 1:26 pm
Even though you are planning to put a hardtail; I would not put a K motor in a sporty frame. I have the opposite -- a sporty motor in a '54 K frame. I absolutely love it. The geometry is a bit different between the two -- and I honestly enjoy the way the k frame handles. If you attend the Wauseon or Davenport swap meets; there is a better than average chance you can pick up the hard parts for a chassis (frame, swing arm, front end).
Now, to answer your question -- unless you plan to title this as a 1970 and up sportster, you want a 1969 and down frame. From 1970 forward, the VIN is the frame . . .creating a weird situation where by you'd have TWO valid VINs on one bike. I'd just assume avoid such a mess and go with a 52-69 frame.