~56, but it's a hybrid, not a MTB, so the geometry is different. Still, ridiculous headtube hah.
Shimming should cause no issues, but Marin made a lot (really, a ton) of quill stems and other components as well, shouldn't be very hard to find a nice one - although most of them are long.
What's the top tube on that?
I'm also trying to find an appropriate 1 1/8 quill or adapter. Is a shim ok?