Found this site :
https://gmauthority.com/blog/2019/07/the-gmc-jimmy-casa-grande-was-a-big-house-on-wheels/ Confirms your numbers of around 1800 made of both Chalet + Casa Grande.
I saw a Motor Trend article that said 225 GMC's were made but did not list a source.
https://www.motortrend.com/news/1977-gmc-jimmy-casa-grande-4x4-camper-auction-mecum/
The Casa Grande at the top of the GM Authority article was the orphaned camper unit — unless it can be proven otherwise — #0855 on a non-original '76 GMC Jimmy where a Minneapolis Craigslist seller in mid 2016 was portraying it as "a rare rust free Arizona truck," implying it was a really nice condition rig with new truck paint … problem is, what I'd seen of it two years prior in a Crosslake, MN series of Craigslist ads was that the Jimmy was a really
rusted heap. However, the originality / collector value of that rig became irrelevant when the 2016 buyer modded it a bunch, including installing solar panels on the roof and upgrading the interior items. Then he sold the camper unit and kept the Jimmy. The camper unit is now seen in occasional internet image search results on a newer modded Blazer where it's all painted up in white / turquoise with '80s-style swoosh stripe graphics.
The
MotorTrend '77 Casa Grande is #1457, repainted the non-original factory colors, a metallic gold and much too vivid of camper stripes colors. The factory main color was a lighter pastel tan and the gelcoat on the camper units was never that glossy. When the shop repainted it back in 2019, they also put on '76 model year stainless steel trim on the truck. The graphics shop doing the vinyl consulted me on the color of the back door decal GMC logo at the time (I could only offer a guess), but that is all, and nobody told me about the truck repaint or other details, I could have headed off that value-killing color choice at the pass. It has a variety of other interior restoration faults, too. The owner who commissioned the repaint told me he redid it in that tone because the factory color combo "was so ugly." However, subsequent sellers claimed it had been repainted to factory specs, one even concocted the line that it was "Repainted to resemble the Casa Grande concept truck in 1977." I told each one of the subsequent owners about the non-original repaint, including the flipsaler guy who put it up for auction at the 2022 Florida Mecum one. He got the "225 Casa Grandes produced" figure from me, but I told him it was not corroborated. 1,780 (the unverified total
from paragraph 2 of this 1979 article) minus the confirmed total by GM of 1,555 Chalets equals 225 Casa Grandes. I really feel sorry for the Mecum auction winner who bid it up to probably more than twice what it is worth, if top-end "like factory showroom new" collector value was the goal for the winner.