Hi there, I would not recomend shackle extensions. You will find if you off road it enthusiastically the springs will break. If you can find some springs with a built in lift you will do well. They are out there but I can't remember the source right now. Spring over axle, I don't think it is a good idea. Yes it enables you to get bigger tyres on it but the diffs are still at the same height and what grounds first. With big tyres the gearing will be shot to bits with only a 1.3ltr engine. You would have to then change your tranfer box for a 410 one or change the internals.
I agree about the shackles I wouldn't recommend them either, i used 2" ones on my pickup and they are poo! They dig in the ground all the time because the are so low and the handling on the road becomes 'interesting'.
There are loads of places to get bits from all vary in prices. Suspension wise give Pro Comp a call, i used them before and they are pretty good, prices are very reasonable too. They do a 2" spring lift system for about £400, thats everything springs, shocks, bushes etc etc
http://www.explorerprocomp.co.uk/ ADK, think his name is Dave, are really helpful i called him for a price on a cage and was on the phone half an hour! But they are in Birdgewater so probably a bit far for you.
http://www.adksuzukispares.co.uk/A good set of tyres is the way forward, I've got grizzly claws going on mine. I had a set on my old 410 (see my pictures) and a small shackle lift , about 1", and it was brilliant.