the premier padmini is just a fiat1100, it still uses the 1089cc engine developed in the 1940/50's (you could use one of these ) however some later 90's models used a fiat diesel engine, this was the same as the uno engine as far as i'm aware, which was also used in the fiat uno and tata indica during the late 90s in india. the engine will fit physically, but the differences mean a lot of work will be required.
i remeber a lad at school who had a premier padmini, he got so much abuse.