Oh, you clever man. Something more obscure than a Bristol in genius.
A Monteverdi. Either the Hai 450SS or the High Speed 375 C (which is quite a cool name for a car).
I thought only Bristol used the LA engines outside of Chrysler (even today, as Bristols use the V10 form the Viper). Hmmm. Though, with further reading it seems that the Sierra was merely a restyled Plymouth Volare, so maybe that doesn't count.