Whilst you're at it, you may as well do the heater hoses and radiator hoses - unless they are already fairly new.
Also a good opportunity to backflush the heater and radiator.
Whilst the engine is out of the car you can inspect the bypass hose - if it's not looking completely new then it won't hurt to change it. Using a piece of solid hose tends to last longer than the corrugated ones, buit installation can be more tricky. To do it without the swearing you can remove the waterpump and slip it in place, but then you'll need a new waterpump gasket.
After installing the new engine - take a little it of time to check it out. Items like the thermostat can be a killer (if it's stuck shut). To check thermostat, start and run the engine - the top hose should stay cold for a good few miles and then get hot when thermostat opens.
Engine mounting turrets can be a pain but i've always managed to get them unbolted when using the right tools. From memory they should be 1/4 Whitworth. Some may have been changed giving a random assortment of different sizes, but the ones held captive by the tie bar rubbers are likely to be the originals.
When removing the previous engine, don't cut off the choke cable - doing this can leave it too short! (the previous owner of my SII traveller did that
) Replacement choke cables were completely useless (I tried a few and then gave up)
Same goes with the throttle cable.
If you're removing the front panel/grille to make the jpob easier, don't forget that the hockey stick studs may be corroded. If they are bad, or if you don't take enough care, you'll end up needing new hockey sticks as well.
)