I fitted new pads and discs to my 145 cloverleaf, and I'm bloody hopeless.
Get some copper grease to smear on the backs of the pads, makes them less prone to squealing.
Can't think of any special tools you'll need, everything is just bolts if I remember rightly.
If you have any vice-clamp thingies (dunno what they're called), they're great for pressing the pistons back in.
Oh - one last tip, dunno if this is likely on the 156, but I know it can happen on the 145 (did to me) - The disc is basically held on by the wheel nuts when it's all together, but with the wheel off there are just two little locator nuts. These break. They're too soft. If they do, don't worry, as long as the head is off, the dosc will still just slide off (if it won't come, prob just rusted into place, give it a smack)
When I did it, I didn't know this, so I panicked and drilled the locator bolts out, which was both un-necessary and meant I didn't have the bolt stub left to rest the disc on, so if you take the wheel off my car the spacer falls on the floor
"Human beings, who are almost unique in having the ability to learn from the experience of others, are also remarkable for their apparent disinclination to do so." - Douglas Adams
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"That's why animals are so soft and huggy."
- Calvin and Hobbes
To err is human, to moderate ursine.