That's doesn't surprise me, the push-to-connect fittings I used for my standard shanks are spec'd for 5/8" BSP. It's all a mystery to me but there we are
Anyway....what does this "non-traditional" shank actually look like? And does the fact that it's actually "standard" change anything?
There've been a number of iron "towers" shown on HBT and at some point they all had to come up with a transitional fitting to accept a short standard shank. Maybe Googling around using site:homebrewtalk.com will help. Here's a random example, you can see there's an iron reducer insert. But, again, that's for a standard shank...
Cheers!