big vibrations!!

G'day - looking for some help if you can advise me about a vibration.
Firstly it's a '63 Signet Vert.

Arrived Downunder early last year. I bought it in April and it needed some work.
Replaced the rear floors and repainted the interior.
Redid brakes and added booster.
Replaced rear uni joint (which was frozen) and repacked front uni joint.
Replaced all tie rods.
Tuned engine.

I have driven it maybe 8 or 10 times for short distances (less than 10 miles each time).

Last week I am heading out to get some fuel. Took it up to around 60 mph before arriving at fuel stop. Got fuel and headed home. At around 40 MPH I suddenly get a huge vibration. Stopped car did visual check of tyres and looked under. See nothing different. Got in and same thing - vibrations start at about 30 mph. Very violent - whole car shaking. Took it to a hill and coasted down in neutral - still there. No vibration when stationary and revving in park. I've looked under it and can't see anything amiss ... except this, the front of the oil sump is very (VERY) close to the K frame. This is a '63 car with a '65 reconditoned 225 slant. I looked at the engine mounts and they look buggered. I have ordered 2 new ones.

Does anyone have a suggestion, please?
Sorry for the long post.