A friend of mine who owns a few 1950's British saloon cars is a big believer in swap like this... As engines in the import cars back then aren't very powerful for driving in North America, especially in non-sports models... I think a fairly common swap is a Datsun 1200 engine (ca. 1970) into a Morris Minor which improves the performance, especially if you want to drive the car on a regular basis... He also thinks a Chevy Chevette engine is a good swap just for reliability sake...
Actually a recent build he told me about, I haven't seen it since I live too far from him where he lives in Ontario... He took a Standard Vanguard Phase 1 (1948/52), restoration to original would have been quite daunting and hardly worth the money, apparently he took a modern chassis of some sort, and after sorting out issues of fit put the Vanguard on top, now again I haven't seen the car but he tells me that the car looks quite normal...