It's the DT, the other tubes seem fine. It's pretty light weight - 1.85kg, and the fork is only .65kg, so in terms of building a light weight vintage bike it's desirable to fix up. It's exactly the right size for me as well - 58cm c-c both TT and ST.

I'll be painting it myself so really only need to spend money on having the DT replaced.

If I wanted to cut it out myself to see the damage, would a frame builder have a problem with this? Andy I see from your pics you did some cutting close to the lug and the ground the remains back to the edge of the lug?