You won't know till you test fit...
I'd suggest 166 callipers with 166 discs (with 5 of the holes elongated to 156's pcd).
There are a number of reasons for this;
* if you mount bracket to original holes then mount 166 calliper as close to those bolts as it will allow the pads will overhang 305 discs by 3mm. The 166 310's should be much closer to being a perfect fit.
* the 166 disc is higher from hub face to disc by about 4mm, this means two things... callipers will be 4mm more inboard so less likely to fowl wheels (or should get away with basic 5mm spacer). Calliper will be mounted 4mm closer to bracket so if spacing them out it'll need less spacer.
With altered 166 discs you'll have better breaking as more pad on disc and the extra surface you gain will be further out, the callipers will be 4mm further inboard which for me means I reckon it'd be very close to fitting under standard 156 17" multispokes.
Anyway hope advice helps. Impossible to give an answer to question as it's not just a case of the offset of wheel but thickness an shape of spokes. If you do get them and need spacers I'd say 5mm or under as basic plate type or if more required then 15mm hubcentric (may get away with 12.5) don't buy 10mm hubcentric as the bit spigot sits round will crack off as not enough material.