Can anyone clarify whether M17 calipers will fit onto Sierra front uprights without a lot of mods being necessary?

Not tried to make a set fit, but I would bet major money they would be no where near.

Nope, no chance sorry.

Sierra calipers are floating single pot affairs. The M16s are fixed twin pots.

David

I did look at doing it the other way sierra to Cortina if I remember correctly the mountings are no where near