Is it legal over there to retro an engine?
Our anti pollution laws prevent retroversion of fuel, exhaust and engine management system, so if your ride is efi you cannot retro fit carbs, likewise you cannot fit an engine say from a 1980 model car into a 1990 model car of the same make, all because of supposed improvement in emmission standards.
The vehicle still has to meet as a minimum standard the rules of the year it was made.
The reverse is permissable, you can re-power an older car with a later spec engine, and not necessarily an engine from the same make, but the conversion must be signed off by a licenced inspector/engineer. Fitting carbs to an originally efi'd engine would score you a failed roadworthy. The same applies to Catalytic converters, if your car originally had one it has to be there, though they never check if it is functional, (yet), there's a bit of an industry cutting them apart, gutting and replacing them to look "as original".
Most later model cars with all the polution gear on eventually manage to pollute more than the original older non pollution gear ones once the gear stuffs up, in my opinion.