Thermostat spacer

I believe you're correct about them being the same for slants. I'm bored this afternoon, and I've been looking for a spacer for you, but I cant come up with anything. I ended up on a slant forum where someone had the same idea as you, but they couldn't locate the correct spacer either.
One of their solutions was to install an in-line fitting in one of the heater hoses.
Keep looking, or maybe someone else on here can help out.
Good luck, Murph