Lotsa of info and picture links seems to have been lost lately. So here is the simple method to modify the upper S14 pan when installing Massive's M2 pan.
1- 1.25" distance from the edge of the upper pan is what you need to clear the threaded bore for the oil vent.
2- On the M2 lower pan, mark a line 1.25" away from the edge. This is NOT where to cut, but you reference
3- Bolt the upper pan on the lower pan with both ends about flush, and report the marks from the lower pan to the upper pan. That's the first cutting line.
4- Bolt the upper pan on the lower pan with the others ends matching, and report the marks from the lower pan to the upper pan for the second cutting line.
5- Cut and disgard the center portion, bolt the small end and the main upper pan onto the lower oil pan, adjust if necessary, and weld.
An S14 oil pump or pick-up must be used for its forward positioning of the suction cup.
This oil pan was designed for M10 and S14 engines fitted in a 2002. It offers tons of clearance all around. You can even move the engine rearward by a few inches for improved weight distribution.
I suggest you cut a gasket from cork or gasket.