Just to be clear: are you sure it's engine vibration caused by the mounts, rather than irregular/rough idle?
With the front side of the car lifted up, you should be able to see the mounts with a bit of effort. You can then use a narrow breaker bar to test the mounts for play.
You don't need to remove the engine to replace the mounts, but it's still a rather involved job.
With a bit of luck you will be able to replace the mounts WITHOUT dropping the subframe....
- lift the car (at least its front side)
- support the engine, either with jack stands underneath the sump or with a support bar on top of it, across the engine bay
- remove wheels & wheel arch liners
- locate engine dampers (see pics below for guidance)
- soak engine mount fasteners: both the top nut connecting the damper to the engine and the bolts that connect the damper bracket to the subframe. Use proper penetrating oil! WD40 may do the job but is not as good as dedicated stuff.
- remove nuts & bolts (a short ratchet spanner AND a ton of patience are your weapons of choice)
- wiggle the old damper & bracket out
- undo lower bolt to remove damper from its bracket
- clean up all fasteners (I either replace nuts & bolts or clean their thread with a tap & die), add a bit of copper grease and put it all back together again.
Some pictures added below, note that I went for the 'DIY route' and supported the engine from underneath.
That made the most sense in my case, 'cause I wanted to have the full subframe out anyway.
You may want to go for support from the top instead, which gives more working space down below...
Those engine support bars are quite affordable (<100EUR), and can often be rented as well.
You could've borrowed mine if you lived closer by!
Supporting the engine.
The black rectangle with the vertical slot above the middle of the picture is the engine-side damper bracket.
You need to loosen the top damper bolt that sits behind it...
The two parts in the top of the picture are the subframe-side damper mounts.
They need to come off to access the lower damper nut.
The parts with the green nylon(?) spacer on top are the engine dampers.
Post-restoration subframe #2
Damper up close.
Note that I re-used mine post-restoration. It lasted another trouble-free 4 years/60-70K kms.