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

Thank you everyone for your support. After sleeping on it, you're right, I can't let a simple vibration make me sell this true survivor with only 44,000 miles on it. Everything is straight on it except the interior is a little tired. But, She's a beauty. Deemo, if you have a trans and will fit my 65 dart slanty, I would be interested in buying it and paying shipping. I need to save up for it first. My 3 spd auto trans slips a little if you don't firmly position the lever on the tree. I'm curious how much you want? I don't know if we can talk prices on the forum. You can private message me at jeffrey356. I will post a wanted drive shaft in the classifieds on this forum.