OK.. Picture of the thingy. Why can't I find pictures of things on the internet.. they have everything. Anywhoooo... hissing, losing air right there.
Poked around under (lots of spiders, not that I don't love spiders, but I don't want to crawl into their home with them), took pics and looked online and etc. Have come to the conclusion that no, they did not replace the transmission with a new turbo 400 (like the guy was bragging). It looks to be in fact an AT540. I'm good with that.
Engine (because said friend said that it wasn't a 350 or 366, like the manual, but bigger engine. The Superior Coach and Chevy Chassis did make a bus in 1979 with a 427. Which I only find references otherwise in Corvettes. Superior Coach officially went out of business in 1980. VIN no ID says that it has a 366.
(Interesting bit of history I also found. Bus regulations came into effect after Oct 1967 incident. Reports said that too much, too thick of, metal in buses shredded children in accidents. Rivets were too far apart to keep panels in place. So mine being one with rivets spread out, I will be shredded in a major accident. Perhaps a good reason to redo the inside ceiling... naw.. )
Couldn't match any casting numbers to online numbers after almost an hour of searching.
By date stamp code D= April (weird) 18, 1979.
Couldn't find this number, not going to tear the valve covers, fly wheel or etc off to look for another number. Maybe another time.