Will be taking engine out. Know I will have to remove engine mountings and lower it to get the top clutch cover bolts etc, but once engine out do I need to leave jack under gearbox; will it support itself or do I need to lower it onto gearbox cross member (which i may need to take off to get lower exhaust section!) Can't remember!

I always support the gearbox. If you are removing the crossmember then you will have no option but to support it. I have used various methods such as axle stands and jacks, webbing straps etc. but the last time I changed my engine I used a piece of 4x2 across the chassis rails and drilled two holes so that I could slide some old head bolts through and into the bell housing. This way I could push and pull the car in and out of the garage without having to mess about underneath.