There is some prep work that must be done on the based on this:
http://www.greytower.com/jon/lotus/europa/gearbox/gearbox.htmlPart of what is described in that link is converting it to a side shifter and you end up with pretty much what Richard at Banks sells (see below). I believe that some have fashioned cable shifters with the original rear shift configuration. There should be plenty of discussion about ways to do this on the lotuseuropa yahoo group (if you own a Europa, you should be a member).
Banks also sells prepared NG3s including a kit for the linkage and all mounting hardware. Look here:
http://www.parts.banks-europa.co.uk/orders_frame.htm and choose 'Gearbox'. This is the route I took and it worked out very well.
In the end, it pretty much depends on how much fabrication you want to do.
Good luck and remember to post pictures!