I can confirm the original fork had a rake of 45mm and that the Alpina is 30. I measured both forks on the bench as I swapped them out.
I added a picture below of my bike when I first built it up. You'll see that with the original 45mm fork there's a ton of tire clearance, so that was no issue.
Now I'm speaking here of the Chinese unbranded, but if you look at the picture you'll see the design of the L size has the down tube rising up then curving into the head tube. That affords clearance. If you look at smaller sizes of the same frame (green bike below, and the smaller 7VRN and Ferocity in my earlier post), that curve is less present in the M and not present in the S. So tire clearance could become an issue as you get smaller.
But as the more math-savvy posters (Carleton? BitingDuck?) can hopefully confirm, when the difference between the 45mm and 30mm rake is 15mm at the wheel axle, that offset reduces geometrically as it moves up closer to the steer tube. Therefore, where the tire would be closest to the frame is needing maybe 3 or 4mm of wiggle room...
Also, it's worth noting that the geometry is not that unusual these days - the Specialized Langster Pro goes with 74-degree head tube and 45mm rake, and you see lots people on those at the track. I think they make this spec because more buyers are getting these to ride fixed on the road than will ever see the velodrome.
https://www.specialized.com/us/en/la...rameset/106261