Does anybody know what the groove dimensions are on a Shadek oil pump grooved for a O-ring. Groove width and groove depth.

Never seen one grooved.

Gene Berg enterprises was the first to do this. It was for a type 1 case. I dont know if type 4 case is exactly the same case width.

I do it on all my T1 Full Flow performance pumps.

I can't/won't give you a groove dimension as you have to measure your O'ring, but I will give you these pointers.
The big one is you only want about .010-.015 sticking up or the O-ring will tear on install.
You also have to deburr the case inlet and outlet holes or that will tear it as well.
You want a thin O-ring that is a hair small so it sits real tight in the groove.
I use DOW55 O-ring lube (ebay $30 tube or you might try a scuba shop for a dab) when installing the pump, it prevents tearing and swells the O-ring after install.

The T4 is harder to do, you have to check all the dimensions and be sure where the O-ring will sit when finished, I usually only do this with the engine apart.
I got a bunch of O-rings from Berg years ago, I only have a couple left.

I thought I once posted this mod but I can't find it.

Note you can not do this to a T4 pump.