Don't run the 34 chainring and the
#1 cog, it isn't designed to do that and it isn't as mechanically efficient as the 50t ring and the
#8 cog. Campy UT cranks are connected with a hirth joint (as you know). No way in the world would I use a spacer that will decrease engagement. Whether Campy says it's ok or not.
It is what it is, no little little and no big big. For the record I run the exact same set up on half a dozen vintage steel bikes.
I get it, you want one tooth changes that the
#1 -3 cogs offer. But with a 16 tooth difference between the small and large chainrings you'll need to learn to spin a smaller gear faster (using the 50t ring) or a bigger gear slower (cadence wise).