While starting over with a Toyota would probably make you more competitive, I went with the SEC. As much as I would've liked to take my 300TD to autox, I figured I'd probably have more fun running the course than driving it.
It's a total guess, but I'd bet the R350 is a pig. Heavy cars are no fun to try and get around the tighter corners. I can't imagine how crappy a decreasing radius turn would be.

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1984 300TD