Removing your melted fork lock won't be easy. I think you would have to drill it out. Normally, removal consists of removing the cover plate then turning the lock to the open position. Then the assembly will slide right out of the neck. The cover plate is all that holds it in when it's in the "open" position. In it's "locked" state, the roll pin sticking out of the side locks it into the frame. I discovered all this while "scrounging" my 1st one. I couldn't figure out how to extract it so I cut it out .....
Once split open, I could see how the roll pin locked into grooves in the neck mount, holding the lock in when it was in the "locked" position. When you turn it to the "open" position, the roll pin aligns with the boss on top of the lock assembly and the whole thing can be slid right out .....
The cover plate is held on by what Yamaha calls a "rivet". But it's not really a rivet, just a short sort of nail with a slightly tapered, swirled shaft. It gets tighter the more it's driven in .....
So, to remove it, simply pry the cover along with the rivet up and off.
There were 2 versions of this neck lock used on the 650s. Both are still available from Yamaha but quite expensive for a relatively unused item. The early version used up to around 1975 had a smaller 12mm diameter body. The later version that came along around 1976 had a larger 16mm body diameter. Yamaha gets around $50 for the later lock, near $75 for the early one. This is why I've taken to scrounging them, lol. There's 3 or 4 more sitting in my dealer's boneyard that I can hopefully "liberate".
And I DID remove that! 
