Big rear window on a 72 - rare option ?

[full foot notch]

So after owning my my 77 and selling it I'm looking to get back into the chevy truck world , I look at the c10s on craigslist and come across this one which he has for $11k (I'm assuming obo )

PLEASE STOP FLAGGING MY AD...im not violating any cl rules

text or email is preferred ...1st...im testing the waters here...I have appraisal papers some place for this truck in the uppers teens....2nd...I don't need help selling this truck

1972 chevy c10.29k miles on rebuild engine truck is a factory short bed, big window work truck. the truck is very rare. there were 2200 produced in this combo for the run of this body style. the truck has a 6 month old bag system featuring fr,bk,side to side, new electric valves. newer stereo, custom yuengling shifter 350 with newer 5spd from a Camaro. paint is hotrod flat black about 6 month old. front disk conversion newer exhaust.not shown in pics.....shaved side markers, relocated tanks under bed..newer and interior pics soon
Bad....exhaust leak...have new gasket, valve cover leak..have new gasket

mostly testing the waters..open to trades..no fwd at all..mostly looking for cash offers or something new...it ur offer isn't in the teens don't bother wasting our times..the truck is rare and I know what its worth

clean California title

I email him asking wasn't 71 and 72 factory disc brakes and he says they were not standard on the base model truck. Me personally I thought they were standard on 72s and above. And I've never really heard of the big window option as all the ones I have looked at online have been a big window. Just asking about these options since I don't know if he's just trying to hype up the truck or if it's truly rare.