Welcome! I've done most of what you're discussing. Do you have any details on the engine and trans? Have you checked to see if the c4 was the one that came off the old "straight" six or if it is for a 289/302? If it was the original trans you're likely to need a compatible bell housing. Which will need to be for a 157 or 164 tooth flex plate depending on your application. What year model 302 do you have?