I have. 1970 DT1 C that looks like a previous Owner has repaired or altered the rear frame behind the rear seat at the rear fender mount.  The welds look crude and are not the same when you compare sides and the fender mounts do not line up.  I purchased a used “rear clip” from a 1970 DT1C and they look similar but are different.  I have a attached a photo comparing the two.  I am interested to know if the rear clip on my bike now is a DT1C or what it could be from. Thanks!

Your frame has clearly been modified from stock, the fender mounts are located higher than original and the triangular gussets that are attached at the curve are not factory Yamaha. The frame clip that you have shown appears to be original and stock. I'd guess that your frame components are still the original 1970 parts, but somebody has cut and relocated the fender mount tabs, plus added the triangular flat pieces onto it for whatever reason - perhaps a custom luggage rack was on it at one time and the frame was cut to fit it. Probably not too difficult to restore, just grind the extra plates off and reweld the fender brackets back on in their correct location by measuring the extra frame you have.

Maybe the previous owner was useless at doing wheelies-- 'like i am'-- & the rear guard has dug in & bent it up. Then its been braced in that position. All a guess of course.

Swoop, Thanks for the thoughts.  That is also what I was thinking, so when this partial rear clip became available, I bought that and figured it would be an pretty easy fix.  

RT325, you may be right!