76 dash in a 74 Dart?

Sender wires for gauges can come out of the round harness connector. put ring terminals on them and attach at gauge studs. Aftermarket solid state IVR can be mounted most anywhere under the dash and attached with ring terminals also.
As for the lamp sockets... I'm guessing you ordered the wrong ones. They come in 3 different sizes. Chrysler uses the 5/8 socket.