Has anyone done this conversion? what do I have to splice and or make? I am also looking for the rear backup light single wire metal sockets that are attached to the wiring harness, mine are missing. they push into the tail light housings. does anyone knows where I can get those. thanks.

There is nothing wrong with a standard dash cluster.

I've done this "conversion", your best to get/download a FSM for the wiring diagrams, it helps avoid a lot of head scratching, the speedo hook up is straight forward, uses the same cable you have, the tach set up will require you to run a wire to the negitive side of the coil, you'll need to either alter/lengthen the ends of the fuel, oil and temp harness wires, your amp gauge wires will hook up with no mods, you'll need to change the engine's oil sender unit over to the "gauge" style sender, and you'll need to get a hot lead over to the clock, the radio plate from your standard cluster will work with the ralley dash, however you need the ralley dash heater control panel, and the ralley dash switch panel, the current switches from your standard dash are the same and can transfer over into the ralley switch panel, generally you'll need the ralley dash light panel located under the gauge ridge of the padded dash, if you don't have it, the standard light panel still fits into place, just that the lighting is not illuminated properly at the ralley gauge pod locations, I'm sure I may have missed a few items electrically, but mark all the connections from the standard dash as you remove them so you don't mistaken the wrong wires/connections, make sure on the Ampmeter hook up that red goes to red, black to black for proper function, as well as making sure the Amp gauge hook ups are properly isolated from grounding out on the dash/instrument cluster, as this is your biggest source of fire/failure

Mike

here's a few pics...

I have an ex-wife who thinks her opinion is more important than actually answering the question.

Mike pretty much summed it up. I'll add that the standard cluster has an oil light so that bulb socket needs the be changed to a terminal for the oil gauge. The leads for the fuel and temp can reach the Rallye gauges with a little finagling. You'll need to tap into the blue ignition wire for the power to the tach.
Is a pretty easy conversion.

RTE makes an adapter harness for this.

https://www.ebay.com/itm/162766275415

Nice to know..Thanks Larry

Thanks for all of the great info, I ordered the conversion kit. One other question I have is the dash frame, is there anything different ralley versus non ralley? I have read conflicting information..

Dash frames are the same.

As noted by moparmarks they're the same, it's the 69-70 B body dash frames that are different when going ralley