1) If these mountings have not been changed within living memory, then the 8mm. bolts holding the cover plate will probably be well rusted in.  You may wish to consider drilling a hole from above into the "chassis" leg on both sides, and pouring in a quantity of burning/diesel/35 sec. oil.  This will hopefully find its way around the threads and rust inside the cavity and help to free them off.

2) A useful tool for loosening these bolts (and any others in a similar condition) is the 12 volt Clarke (Machine Mart) Impact Driver, fitted with a suitable mono-hex impact socket.

3) Even if these bolts are impossible to free off, the threaded hole they screw into is comparatively short.  Shearing off the bolt head then drilling and tapping a new thread is a viable (though awkward) option.  Use Coppaslip when re-assembling, in case you need to do this job again.

4) In the absence of a pit or ramp, you will need to support the car with the rear end elevated, on axle stands.  Use at least 2 in. x 2 in. square wood, maybe 4 feet long, to spread the load along the length of both cills.  Remember - Safety Assessment At All Times!  Front wheels chocked, car in gear, level ground, rear wheels beneath cills as a precaution.

5) The following will need to be either removed or loosened off: rear silencer box; lower shock absorber mountings; Panhard rod lower end; rear wheels; the head of the upper O/S shackle bolt is accessible by removing the spare wheel, and prising out the big grommet in the spare wheel well on the spring side.  Also: dislocate the lower end of the levers from the axle to the brake balance limiter on 2000, Fulvia S2/3.

6) It is almost impossible to lift the rear axle exactly where it balances, so that it and the rear end of the car rise level.  Consequently you will probably need to raise and lower the axle in order to find a position where each shackle bolt is free enough to be prised out.  When removing the upper shackle bolts, look out for 2 off steel rings fitted either side of the bolt., between the shackle plate and the mounting block.  This is part # 82302027.  There was a recall from November 1972 when new shackles (part #s 82302026 & 82302027) were supposed to be fitted to all Flavias, Fulvias and 2000s made up to then, in order to avoid fouling of the upper mounting block cover plate when on the move.