[rx4ur7]

Whole car shake OK. If it were a stock vehicle never worked on I would first go U joints. Trans mount can cause issues, as can rear diff mount. Although rear diff mount was usually the complaint that the rear was trying to come out from under the car on take off.

If the clutch has been replaced, loose flywheel, loose clutch cover, broken clutch cover especially if it was a rebuilt unit.

60mph is the usual range for tire or wheel related vibrations. And you can usually know if it is front or rear by steering wheel or seat feel.

U joints should be obvious. You could remove the driveshaft and see if the shake goes away. If it does, driveshaft or rear. If it does not, motor, clutch, trans.

I have had a vehicles come in that had clutches done at a quick clutch place or just a general shop that had flywheel clutch issues. One the flywheel was loose, one had missing bolts on the clutch cover.

I had issues with whole car shake in the GT car, a bit unnerving when going through turn 12 and 13 at PIR in Phoenix. Needed to have the split driveshaft installed, once I did that I could run flat out through them. Then it was just - hope the Goodyears stick, and never cross that white line at the apex.