Re:
I had this problem....
As far as I can make out....(with my limited retro modern build experience) this is one of the issues that is common in retro - modern builds.
I did warn you there would be more challenges ahead!
I ended up drilling and tapping.
If you have a drill and tap... it's a doddle. Tap sets are cheap as a packet of Fish and Chips.
Also used spacers but that was more about chain rub on the rearstay. Those alone would not have solved my problem with clearance anyways.
Am doing an update on my Gillott build soon...but here are some photos to illustrate how I got around that particular problem.
Note the drilled and tapped hole with the hangar retention bolt in place.
It looks closer to the cut-out than it actually is, around a 2mm clearance between the drilled and tapped hole and the dropout cutaway.
Sure...it puts the wheel back an odd mm but it works fine.
Post assembly. You see how tight things are around there...and that's with an additional 1.5mm of spacers on each hub.
If you use spacers....consider placing them on both sides to maintain your dish/alignment.
And as a final piece...check your hangar alignment after you finish everything up.
It's an absolute doddle if you have a spare wheel to hand that is threaded. Screw it into the derailleur hole, thereafter it acts as an alignmnet guage and with a small effort a re-alignment tool! See below. Yes it looks odd but it works an absolute treat and is a must check prior to setting up the indexing etc. etc.