The pressure gauge sender & oil pressure light sender are 2 different units.
They screw into the engine in slightly different places, but very nearby to each other.
Look for a blanking bolt angled downwards at 45 degrees near to where you've seen the straight out sender.
Does your car currently have a cluster with a tacho? If not, you're in for a lot of rewiring to change it. The plug are the same, but lamost no wires are in the same position.
If you do have a tacho cluster, then it is very simple to upgrade to the oil/volts cluster. The wires are the same, but you'll be missing the wire for the oil pressure gauge.
Once you have installed the proper sender (just leave the old one in to block it hole blocked up):
- unplug the wire for the pressure light sender & plug it into the pressure gauge sender
- remove the dashboard cowling & instrument cluster
- find the wire that goes to the oil pressure warning light & cut it
- find the pin on the back of the oil pressure type instrument cluster where the wire comes in (you'll probably find that position in the plug is empty)
- find a piece of wire with the correct pin end to suit the plug (trip to the wrecker?)
- join this to the wire you cut for the warning light
- reinstall everything
I'm not sure if the cars that had the gauge also have the warning light or not, but note that this method means there is no more warning light, just the gauge.