Small Block & Big Block Chevy Specific - Oil pressure sending unit???? NEED HELP

I am helping my friend install an oil pressure gauge in his 1972 chevelle 350 . . . what we need to know is where is the oil pressure sender so we cn connect to the gauge. Anyone know this or know of a guide we can follow for a 350???

Thanks

There is 2 places they put them. Right behind the distributor slightly off to the drivers side on the block, right behind the intake manifold. Also, some can be by the oil filter also.