Looks like a first gen Coffman 650 SX/X2 pipe. The chamber looks steel instead of the later cast aluminum. Head pipe looks like a second gen Coffman head pipe. The first gen head pipes were steel as well as the chamber.
If you use a 650 manifold, you could use that pipe on a 750 if you wanted to. WestCoast sold the same modle pipe for 650 SX/X2 and 750 SX but they used a U turn pipe to make it work on a 750 SX.
I hope that helps.