Will a lowering kit or springs from a mk3 polo fit a mk2 polo ?

yup all exactly the same suspension wise!!

^^ What he said,even though the MK2 is lighter.

Isn't there a slight difference in struts, although everything still bolts up?

yes if your going to be pedantic the part where the hub is joined to the strut body is beafier on mk3 than mk1 and 2

but fitment wise its all the same!!

so a mk2 one will be lighter..... ?

yes if your going to be pedantic

That's me

Here's some pedantry -> The late MK2 is the same - MK1 and pre-'85 MK2 had the far smaller (but thicker) box sections,whilst post-'85 cars got far bigger box sections that carried over to the facelift car. :)