there's no real NEED for the disco engine mounts unless the original 2a mounts have already been cut off, although some folks DO fit them and claim a vibration reduction (i've no personal experience myself)
my engines sit on standard Series petrol engine mounts (round ones) with spacers to lift the engine a little more, the only time i suffer a little vibration is when the engine is idling, lift it just off idle and it smooths out nicely
others recommend genuine 90 mounts to assist kill the vibration (the one needs a little trimming with a slitting disc), these bolt on using standard Series chassis mounting points (again i've not fitted these myself as it was after i built my conversions that i found about them)
the bonus in my opinion of using standard mounts is it makes it a simple job of reverting to a standard engine should you wish to, or should a potential buyer wish to at a later date
anyway good luck