Pulsating vibration while cruising??

Hello guys, i'm looking for tips on where my vibration could come from.. it usually comes when driving over 40 mph, often while giving gas. seems to go away when letting go of the throttle, really hard to know (pulsating kinda speeds up when letting go). I have a 69 dodge dart with an 8 3/4 3:23 rear axle, new balanced wheels and strange drivetrain, new mounted yoke from strange. Does not vibrate when in park or at slow speeds. i have a 70s 360 with xe274H cam, new motor mounts from schumacher, used trans mount but looks good. exhaust is 14 inch magnaflows with dougs headers. As already said its a vibration that comes in pulses, a few seconds long. vibration intensifies when accelerating over 1800-2000 rpm

I have concluded with two things: the yoke is not properly mounted or the converter is missing a weight as i figured out externally balanced engines needs this.

Let me know if i'm looking in the right direction.


thanks