Plymouth Duster of 73

Thats awful you cannot put a different size engine. The duster is sexy looking, it needs MORE POWER lol. Can you modify the existing size engine? Bigger bore, longer stroke? Hotter camshaft? Fuel injection? Turbo? Supercharger? Lots of people on fabo souping up the slant 6. It can be made as powerful as a V8. Are you allowed to replace the engine, if you are putting one of the same kind back in?