When these bikes were not worth much and guys were giving them away I raked a 750. The lower of the three top frame tubes were already cut near the front. I took two widths of masking tape out of the main backbone tube and put a come along on the top of the neck. Then heated the front frame vertical tubes equally just below the welds while pulling the neck back. This method moves the tank mounts back so you need a smaller tank or move the mounts and seat also. I tig welded the main top tube and also put the lower ones back in. I never finished it and didn't ride it.
That frame is late 70 numbers with a 71 title, bad Don. I am working on a frame jig and plan to return it to original specs.