thats your oil pressure switch. your motor will spew oil without it plugged. your best bet now is to have the hole plugged or welded up and run a oil filter sandwich plate with a npt fitting for your oil pressure.
i the second pic it looks like there might be enough thread to put the sensor in and not have it leak. I personally wouldn’t do it. From the looks of the pics though the block is out of the car, I’d call this block done and find a new one. If it’s a dd, throw it back in and see if she leaks.
plug it and you will be fine. same thing happened to lazy’s motor. But remember your motor will see probably 70-80psi+ of oil pressure so however you plug it make sure its a good fix.
You might be able to get away with a bolt and some jb weld to close it up. Make sure you have the thread. And as far as welding it not sure if anyone is going to have a portable machine to weld aluminum but maybe.
going to a gsr block if this fails, i got this block on the cheap, and its bored and has pistons. So if I cant find a way to plug the whole, im just gonna build a gsr block. thanks anyways.
i would just get a bsp (its british standard pipe taper thread not NPT) plug and thread it in there with a bunch of teflon tape and see how it fits. Then get the filter sandwich plate as previously mentioned.