The little vent doors on my 70 K5 are designed to come out in order to clean behind them. The top pivot pin is spring loaded, just open the vent door all the way and gently pull in on the bottom of the door, the whole door pops out. I found this out trying to get the mouse house out from behind the vent door. Also, I pulled the backs off my util buckets and found the OE tags on the seats, with a date of 22 Dec 1969. Either my 70 was built really early in 70, or GM had quite a stock of seats. Thats all, just stuff I found interesting.