oil pressure

how much should the oil pressure be on an 82 280zx? my dad got me one for christmas. we completeley gutted out the interior and replaced it. its in great condition, but it seems as tho the oil pressure is a little low on it. oh and the mount for the rear differential is missing, so every time I shift or give it some gas it thumps the bottom of the car. I'm thinking about removing the catylac converter and running a straight pipe, would this be a good move? my dads friend at a mechanic shop said it would add power and allow better air flow. let me know wat you guys think