I am looking to buy brake calipers for a frame. I have read and understand the measurements needed for brake reach but wondered whether the mounting bolts are a standardized diameter and length or if this varies and if so can be switched out?

Rear brake bridge width = 35mm
Front/Fork crown brake bridge width = 42mm
Brake reach = 45mm

I mock fitted some Shimano 105 (1050 series) to the frame whose reach was just adequate but the mounting bolts were much too short.

TIA!

EDIT: looking for recessed brake calipers