I dunno about an actual unit for you, but you could continually check our Parts for Sale section of this site for a unit that becomes availible. Anything from 70 -> 72 will fit and it can be from a Chevelle, El Camino or Monte Carlo. 70's have greenish numbers/letters (more rare) while 71 & 72 have white. Expect to pay anywhere from between $150 -> $450 depending on if the harness and PCB (printed circuit board) are included.
I converted my old dash harness (which was really hacked up) from lights to gauges. If your harness is in good condition, please consider leaving it unmolested and using another harness. That way, if you keep the lights pod and harness, your mod is completely reversable for a concours resto for you or the next owner. I still have my original lights pod for this reason.
For my notes on the subject goto:
http://azonline.com/~jimmy/conversion.htm
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??michael j Team Chevelle Gold #77
70 Chevelle SS396 4sp, Fathom Blue/White Stripes - Canadian built