Install? No. Run? Yes.
I basically attached my A1200's HD to my 4.1 box and copied everything over. Other than temporarily renaming the odd application configuration file here and there (usually to stop an application trying to open a screenmode from my old system for which there is no matching displaymode ID on the new one), most stuff just worked.
As an aside, rather than make a mess of the system partition by dropping OS3.x libraries etc into it, I have an "OS3.x" directory in my main OS4.1.2 partition that has subdirectories for libraries, classes etc. into which I assign add in my user startup. This keeps a degree of segregation between legacy 68K stuff an PPC native.
