Cylinder numbering has been the same on all Subaru flat 4's I have owned.
Looking from the top, from the front of the vehicle, you can see the side to side cylinders are offset. The right side ( left as standing in the front ) are closer to the radiator. Using this as a guide, start with that cylinder as number 1.
The next one back is on the other side, left ( right as standing in the front ), that is number 2 .... next back is 3, and finally 4 is the rearmost.
This is also true on the H6 ..... closest to the front in number 1 .... and so on.
Always has worked for me .... in over 30 years as a Subaru owner.
98S, 2014 Impreza 5 dr Ltd (9 Subaru's since 1978, 7 were 5 sp) ILuvSubaru's