Hi Stephen I asked the same question late last year. Here is a copy of Bill Davies' reply:
When fitting a new engine mounting, be sure to loosen the one on the opposite side as well. Fit the new mounting stud into the engine plate first, then loosely fit the 2 bolts. Start the nut onto the mounting stud, but don't try to tighten to any degree - there should be plenty of scope for movement. Tighten the 2 bolts on each mounting so that there is just a little play, maybe half a turn of each nut before they become tight. Now lower the jack gently. The engine will rarely settle properly as it drops, so you wil need to grab the rocker cover and rock the gently on and off each mounting. Everything should fall into a stable position, so you can now finally tighten all the bolts followed by the nuts onto the studs.
p.s.
I also found access to the n/s mount attachment was made easier by removing the radiator bottom hose.
Good luck.

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Engine mounts

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Engine mounts

Engine mounts