It is not at all difficult to do the A15 transplant providing you have got some common sense.
First thing to do is to see what engine is currently in the car. If there is an early model A series you will need to either make some brackets to mount the new engine to the original
engine mounts or mod the crossmember to fit to the new engine. This also depends on where you want the engine to fit in the engine bay which will determine whether you need a different
gearbox mount. If you keep everything as it is and just fit the engine there will be no other probs apart from making the brackets or changing the crossmember. Ask your authorities
before making the brackets as they may not allow them.
If this is the case I have a crossmember that was made on a jig you can buy.