The OAG-L and ASI2600 are not mutually compatible.
Both have M2.5 holes, but the tapped holes in the camera are spaced 60º apart, while the OAG-L's four holes are tapped (at the same 31mm distance from the optical axis) with 90º spacing.
If you insists on using the OAG-L, you can drill and tap four extra M2.5 holes in an extra ASI2600 tilt plate. You can drill just two extra holes if you don't care about placing the prism at the long axis edge of the sensor (you can mount the OAG with just two bolts too, but I won't recommend it).
You may also need to liberally apply electrical tape to prevent light leaks when you mount the OAG directly to the camera's tile plate.
Also, be ready to remove an extra 15mm from your guide camera's flange when you mount the OAG directly to your camera, since the guide camera is now closer to the main camera (filter wheel 20mm minus 5mm for the extra tilt plate).
Chen
