Yes, 20SEH is the GM name for the engine, it is in the SRi 130 here, as well as early Vectra A/Astra etc so it was fairly common. The 115bhp version is the 20NE or 18SE.
If you plan on fitting the injection engine as phase 2 make sure you plumb in two fuel lines from the start. Oh, and fit the front brakes from a 2.0 Vectra A as well.