Easy way to check stack height:
https://www.flickr.com/photos/282672...7625424641013/
Honing isn't a very efficient way to reduce the fork crown race seat, nor is filing.
The best way is to find a shop with a fork crown facing tool and someone who knows how to use it. It's worth having the fork crown refaced, also the top and bottom of the head tube.
If you can't find a tool with a 27.0mm cutter, have it cut down to 26.4mm or 26.5mm. The smaller size crown races are easier to find.
27.0mm was the French standard for crown races. It's also the Japanese JIS standard for track bikes plus a lot of Japanese bikes like your Miyata came with that size crown race too.
The Stronglight A9 headsets are bulletproof. They're still available: new and used ones are listed of eBay all of the time. They were available with 26.4mm and 27.0mm fork crown races. The 26.4mm are the most common size. They have a stack height of ~38mm.
There are 2 new styles of Stronglight A9 headsets. The tapered bearing style has been dropped in favor of ones with precision sealed ball bearing cartridges. They look the same as the old tapered bearing style A9s.
I installed one of them on a bike and it's smooth as silk.
The other new style A9 headsets are made of black colored steel (probably painted) and have caged ball bearings. They're crude compared to earlier models. They're selling on eBay for low prices - you get what you pay for.
IMO, the simplest solution would be to go with a Tange headset. I've never seen a failure in any of their better models. They make a number of different headsets but these 2 are very good:
Tange Levin CDS has a stack height of 33mm with out extra spacers. They are through hardened alloy steel with precision ground races. They also have plastic dust seals. They're available with both 26.4mm and 27.0mm crown races. You have to shop around for the 27.0mm ones. They've been selling for $15.00 to $30.00.
Next is the standard Tange Levin headset which looks a lot like the old Campy headsets but MUCH better quality. They have a 38mm stack height and have loose ball bearings. they come in both 26.4mm and 27.0mm but you'll have to hunt around for one with a 27mm crown race.
Headsets are one of those things on a bike that I like to set and forget. I recommend getting the best one that will work for you.
VeloORANGE alloy headsets have a 41mm stack height which is the same as the old Campy headsets. They only come with 26.4mm crown races.
BTW, I've never seen a Campy headset with a 27.0mm crown race. Even on French bikes, they were 26.4mm.
I have a prototype Chris King from the early 90s on my off road bike. It's still working flawlessly.
verktyg
Chas.