No, it is a junkyard engine because the original was blown up at some point. Buick started painting their 455 engines that blue color (as did the rest of GM for corporate engines) in very late 1975 and continued on through 1976 (and beyond for corporate GM engines).
The owner says he never puts the windows or the top up. They have been down permanently since 2005. He also says there is no belt on the AC compressor and the heater core is bypassed.
I've also found that people will paint the engine different colors because they don't know any better or care. The valve cover looks more like a 72 than a 75+.
