HELP NO OIL PRESSURE!!!

[fiveohpatrol]

what could cause my car to get no oil pressure from just putting my heads back on? i drove it earlier and i seem to remember the pressure was a little higher than normal and then tonight i drove it and the oil pressure needle was all the way at the bottom, also because of no oil pressure my rockers were making loud noise, i put a friends sending unit on and that didnt help, i also made sure the oil pump driveshaft was still there, what the hell is going on?

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88 Notchback 5.0, 3.73's, Ported E7's, Explorer int. w/ ported lower, pulleys, Crane 1.7's, BBK headers, off-road H-pipe, flowmasters, subframe connectors, 65mm TB, shift kit, March ram air kit, motorsport wires, MSD coil, upper and lower control arms, 155lph fuel pump, cheap 2800 stall, Crane Adj.FPR, best time- 13.99@99.75, not yet tested times after rockers,intake or ported heads