ok so should I go for http://www.minisport.com.au/prod618.htm or http://www.minisport.com.au/prod2041.htm?

I am thinking the first ones?

Have also found these

ebay uk?

http://www.ebay.co.uk/itm/SET-OF-4-CLAS ... 416e171dbc

These are correct, the others from UK RLJ10001 are used with the stepped brake drum

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" A Hundred Years From Now It will not Matter what my Bank Acount Was,
The Sort Of House I Lived in, Or The Kind Of Car I drove ... But The World May Be A Better Place
Because I was Once Important In The Life Of A Child"

Running Discs

These from minisplus

http://www.minis.com.au/minis/catalog/p ... cts_id=970

While I am replacing the studs i think I will refurb the calipers as well.

How often do the pistons need replacing? Since I will be ordering before I get to pull them apart are they an item that is a most likely to need replacing or are they a rarely ever need replacing item?

Original S caliper pistons were hard chrome plated, they don't wear really. This plating was fine when new however when they get old, corrosion can come through as pits.
Have a look when you remove them...
S/S replacements are common, but you can still get chromes ones I think.

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.