Stumble? at 60+

What is vibrating? My 66 Valiant 225/903 with a rebuilt front suspension feels really solid at speeds up to 80mph?
I should probably change my username, the car is a 318 now. The front of the frame isn't exactly straight, which is responsible for some of the vibration. Also I put in a 8.25 axle and am not conviced that the pinion angle is exactly on. Learned a lot from the swap and I need to get back underneath and pretty much re-do the install to get it perfect