FWIW the bike ran fine the years I owned it. Started easily, and had performance about equal to other 160s I'd heard about. That bike got ridden pretty hard from the word go and it never missed a beat.
According to the linked post (I don't remember this stuff almost 6 years later) I took off about 0.6mm, and then had about .3mm clearance between the clips and the collar, I doubt there is 1mm there normally. It didn't seem like a major deal, certainly nothing that would make the compression skyrocket. A little bird told me (Fine, it was Tom Bailey's singles buyer's guide) that high compression pistons aren't readily available for the 160 anymore so the trick path to high compression is to take 3mm off the base of the cylinder. The change I was dealing with wasn't anywhere near this and wasn't going to hurt anything. The piston wasn't hitting the head, the valves weren't hitting the piston. The bevels were shimmed correctly going by the stepless planes and I couldn't feel any play in them. Most everything in that bike was original to that engine aside from the gaskets so I doubt any spacers were wrong. I spent time checking things over before I trimmed the collar. The base gasket was the likely culprit unfortunately the engine had been apart for about 4 years at that point and I didn't have the original around to compare anymore. I've seen .8 and .4 listed as gasket thicknesses (a quick google check two minutes ago) and it seems plausible to me that if the original was in the .8 range and the replacement .4 I could easily have run into this situation.
But now I'm rambling. Bottom line, trimming the collar wasn't a knee jerk reaction, there was thought and investigation involved.
As for the case being clean, maybe the pictures made it look better than it was? In real life it wasn't any cleaner than other aluminum cases I've worked with. I have no idea how many miles were on the bike but it don't recall the interior looking any better or worse than "normal". Here's before and after shots of a roundcase I rebuilt, it was in slightly worse shape than the 160.
As Eldert mentioned, that bike has been sold and now spends most of it's time more or less on display with a bunch of old Porsches and other cars being worked on at a local import auto shop. A few times over the summer the new owner took it out and rode it down the street in front of the shop but that's the extent of the use it will see. The Wilcox bodied bike he mentioned is stalled now, long story short I've gone back to my roots and bought a car project. 1931 Ford Model A chassis with a 1927 Model T roadster body. Speaking of which, if anyone has a turtle deck for the 'T, I need one...