Mystery vibration at 25 mph can't be diagnosed. It's not the front end!

I agree about the rake. It drives me crazy! It's not the 1970's. I found the proper 5 leaf springs right away. I think the previous owner put them on to look cool or something. Before this vibration issue became a nightmare, I had found the proper 5 leaf springs and was going to put them on. Now the ball will be back in my court and I will take my time and follow all advise. I'm really not as dumb as I appear, I just became the middle man in this affair and the mechanic wouldn't follow my leads. Everyone is plug and play these days. Knowing your old car is the best way to go. I agree with Dan, but was between a rock and a hard place. No more. The dart just purrs after I switched to electronic ignition and has only 43,000 miles on it. No smoke out the exhaust at all. Thanks everyone for your advise. jeffrey