I live near West Of Pecos (RIP), the birthplace of the Rodeo Ghost. I frequented this restaurant just for this cocktail.
A few notes:
It was never served up - rocks glass, huge ice cube
The Rabarbaro amaro they used was Zucco, probably due to availability. Curious about Nardini
The sweet vermouth was always Carpano Antica
A few years before they shuttered, they switched the orange twist for a big grapefruit peel and it made a surprisingly big difference.
I love this cocktail so much. Please make and enjoy it