Mystery shudder

Thank you guys, I think I solved the mystery..... Bad miss-fire on one or more cylinders.
I changed the HEI module and went for a ride around the block. Same shuddering and bogging.
Then when I came back home, I didn't turn the light on in the garage and open the hood. Looking careful at the cyl.1 I could see spark arching to the exhaust manifold.
Because the driver side manifold for these early darts is really tight and going up before merging into the exhaust, I used some short sleeves cut from longer heatshield tubing with velcro to protect the wires. See the picture. I didn't realize these heat sleeves are good electrical conductors.
So a combination of maybe one or two bad spark plug wires and these sleeves getting in contact with the ex. manifold and the wires at the same time just created a path for the spark to go haywire.
Tighten up the spark plug wires, took all the sleeves out and went for a ride again. No more bogging....
Time for some good spark plug wires and some spacers to keep them away from each other and from that ugly manifold. Lesson learned.

Thanks again for all your help.