I'm not sure how well that old three speed will hold up to a 350. If your heart is set on the swap (which sounds sweet), then go to www.advanceadapters.com. I've never tried a swap from a straight 6 motor to a v8. Most likely the motor won't bolt up to the three speed. Advance adapters makes all kinds of bellhousings and what not. They make adapters that will bolt a chevy motor to a ford tranny! So I'm sure you'll find something.