My wife purchased an Ultegra 8020 groupset for my birthday present. Unfortunately the brake calipers do not line up with the mounts on the frame, fork is 74mm, frame is 51mm. Are there adapters so I can mount the Shimano brakes? the holes on the Shimano mounting plate are slightly closer than 74mm.
You might want to start by checking out this thread.
The Ultegra brakes will be flat mount. It sounds like your frame has an IS mount, and your fork has a post mount. AFAICT, there is no such thing as an adapter for flat-mount brakes on a post-mount fork, nor for flat to IS. Yay standards!
This gentlemen https://www.assolutions.ca/shop/adapters out of Edmonton does make adapters for flat mount calipers onto post mount and IS framesets. I have ordered one of each for my Kona, and will update once I have them installed. According to his 1:1 scale template, I should have the clearance for them.