The person behind Multi-Safari has documented the procedure to create a Safari application with a self-contained WebKit framework here.
Basically it involves duplicating the Safari application, opening the contents and creating a Frameworks folder inside, copying the Framework from /System/Library/Frameworks and then performing some jiggery-pokery to get the application to prefer to use the self-contained framework over the one in the Library folder.
(I decided not to copy his instructions word for word, as his website didn't use Creative Commons.)
Best Answer
No, but you can install an older version of OS X in a virtual machine to use Safari there.