This from one of my favorite sleeper writers Ed McClanahan:

"It was a totally crazy project. About five years ago the Smithsonian started talking to Ken [Kesey] about how they wanted to get the original Merry Prankster bus for their collection--they literally wanted the whole bus. But the original prankster bus has been sitting in a swamp out behind Ken's house for years. It had grass growing in it; it was totally immovable. So he [Kesey] said, "Well, the original bus is in ruinous condition." And the Smithsonian replied, "Don't worry, we will renovate it; we will bring back to what it was." So Ken explained, "Why if you're going to do that you would have to renovate it aU the way back to yellow, because originally it was a yellow school bus!" And there is also the fact that there is no original bus in a sense that it was changing all the time. They would paint it wildly psychedelic one day and then go paint it black the next day if they had one particular event they wanted to have a black bus in. And immediately they'd go paint it wildly psychedelic again. There were places on that bus where the paint was literally over an inch thick. So Ken told the Smithsonian that "there is no original bus." But they kept insisting on it. So he went and bought a "new" bus; it wasn't at all new, though. I think the original was a 1939 International, and the "new" one was a '47, I believe. It looks pretty much the same, except that it is smaller, and very much in better shape than the [14] old bus ever was. It was a nice, tight, ready-to-roll little school bus that had been pretty well maintained. Ken redid that particular bus. And they did just an exquisite paint job on this version of the bus. It was truly beautiful inside and out--it had an astonishing sound system--all the stuff. So Ken did this, and did it secretively. And he pushed the old bus even further into the swamp and covered it with camouflage cloths, and declared to the Smithsonian that he was going to bring them the bus. This was all a hoax. It was all meant to--well, it was a giant prank. The Smithsonian very emphatically declared that it didn't want a reproduction; it wanted the original bus. Ken declared that despite that fact, he was driving the bus across the country for one last trip and intended to present it to the Smithsonian. And they kept saying, "We don't want it!," and Ken kept saying, "It's coming anyway!"

Check out the conclusion:
http://history.hanover.edu/hhr/95/hhr95_3.html