The single unit combined high-low Power Beams made their debut on the 1970 Camaro / Firebird & Monte Carlo.  At Chevy they took over for the T-3 for 1971. They had the diode symbol in the center. Some Pontiac pictures show the T-3s with the triangle emblem on promos as late as '72, but remember the timeline for these promos in the studio & using the parts on hand (like lights). A '72 front end shown on the LeMans brochure was probably in clay back in early '70.

I have a set of 4 brand-new Power Beams for a 4-light setup in the box that I bought years ago from a Chevy dealer back around 1992. They parts guys brought me the dusty boxes and said the last time they sold them was 7 years prior. Later when I realized I should go back & get a set of the large combined high/low beams as they would be  nice touch on any restored 70-81 F-body, but the remaining stock had been cleared out & sent to Colins Automotive. I checked at Colins & they were out of stock. Gone.

I pulled a complete working set of T-3s off my '67 & stored them. I remember back in '70 when dad's new Biscayne took a rock to the headlight that broke a T-3 & that is why I went to the dealer for Delco replacements in '92 when I put the Chevelle back on the road. I ended up running GE halogens anyway since that is what the GM parts counter had.