I bought a new 1" threaded 105 headset for my 88 Japanese Bianchi. I put on the cups...all good so far...go to put the race on the fork...hmmm its resisting. I take it to LBS and the guy says this is 26.4 and you need a 27 for your fork. Look in the catalog and see the Deore headset utilizes a 27 mm race. He calls Shimano and they tell him they are incompatible. My question is what to do now...

Remove cups and sell headset for a loss - I hate this idea.
Try the Deore race anyways - Risky and the the race alone is 14$ !!
File or mill the fork down until the 26.4 mm race works - I have no experience, hope someone else does
Drink a beer and stew

This is obviously my first time doing this, and I really wish the shop I bought this from would have at least asked if I knew there were differences...I would have measured the fork to make sure!