Thanks guys, nice to have you alls support
I was really feeling like a idiot not being able to get this sorted out, which is why I punted to the shop. Luckily I have got a good place to go to, not sure how he could let me out the door for free...
There isn't a real reason for the matching number carb other than I started down the road getting a new carb and decided on getting one that matched the truck. This getting a new carb goes back to May 2020, since my brother wasn't 100% sure how well he would be able to rebuild the '78 one (he never worked on a Quadrajet before). So I decided to go top self and not to cheap out. Funny thing, my shop guy says the one my brother rebuilt was/is running perfectly and describes driving my truck as: "it drives like a
new old truck with your old carb".
Thank you for the offers on other carbs ... I am not sure if I have the stomach to spend more cash on another carburetor....
PS: On the upside I can swap carbs in like 10 minutes now.... I don't even forget a clip or a vacuum hose anymore ;-)