How about the little Buick Alum.V-8 from around 1964. Land Rover according to the Hot Rod magazine produced it up till a few years ago. Performance parts are also available for it.
Funny you should mention that. I was just speaking with a gentleman at the car show in Nashville Saturday about that very motor. My shop teacher in the mid 70's had a Triumph Stag with that engine in it. According to the guy I spoke with Saturday yhat engine was a 3.5 liter all aluminum V-8 originally made by Buick. One of those properly built with twin turbos should do a nice job in a SS.
A little more info on the the little Buick 215 Alum. engine from 1961. Rover did use the casting up until a few years ago. It was also used in the Indy 500 by Mickey Thompson in 1962.
I had a 1961 Buick Special with the 215 ci V6 and Powerglide auto trans. Great little engine, except for using iron cylinder sleeves in an aluminum block. being an ignorant teenager, I ran straight water for a short period and the galvanic reaction between the aluminum cylinder block the iron cylinder sleeve quickly ate a hole in the head! Befoe the head problem, that thing would go like a bat out of He..!
Oldsmobile offered a version of that engine, too. See - Oldsmobile / Buick aluminum 215 V-8 | The H.A.M.B.