Aftermarket gauges

Hope all is well with everyone first and foremost. So I purchased a set of gauges, not to look cool so I’m hoping I can get them going. The gauges are the typical water temp, oil pressure and volts. The volts are by far the easiest, the water temp easily figured out (hope I didn’t speak too soon) but the dreaded oil pressure has me stumped, can someone please help me figure this thing out. The motor is the original 273 with original manifold and original radiator. Any help would be greatly appreciated. Thanks is advance