Thanks for everyone's input. I have texted the seller saying I have a case of "non-buyer's" remorse and waiting to hear back from him. He's a friend and the Whizzer isn't publicly available so I'm sure the opportunity is still on the table.
In response to some of the comments, I've never been afraid of dirt, grease or hard work and I have built my share of engines over the years. I am pretty good with bike and bike parts values, but project Whizzers and Whizzer parts are out of my wheel house of knowledge on value. I know what I can get a entry lever "runner" for and I feel like if the engine on this one is serviceable I'll come out ahead because I have all of the conventional parts to put the bike itself together. I wasn't looking at buying it from a "part it out" perspective but knowing the value of the bits and pieces exceeds the asking price is comforting if I do get into the engine and find that it is too far gone.