On the LH (oil filter) side of the block there are two holes tapped to 3/8-18 pipe threads. One is used for the oil pressure switch. The other is there because a cross drill is needed for the oil feeds. The extra hole is simply closed off with a pipe plug in it. So this one is available.
On the RH side of the block there is another cross drill. This has a 1/2-14 pipe plug in it. Only issue is that this is farther downstream, if you will, from the oil pump than the extra hole above.
