I’ve got some shiny new See cranks, and 3 plastic spacers and 2 metal ones.

Now I’m presuming the metal ones are pedal washers.

Where do the plastic spacers go? – there are no instructions 🙁

It’s to go on a 68/73 bb….

They’ll go between the cups and frame depending on what chain line you need

which do you have a 68 or 73mm frame?
http://www.hopetech.com/wp-content/uploads/2014/03/BBinstructions.pdf
Instructions here, but the spacers should be the same as the one you removed.

73, and i’ve just removed the old cranks and with that diagram it’s clear. Thanks!