I take you've decided the existing system isn't worth fixing?
4.2 will gas up nicely. Make sure whoever sells you an injection gas system knows its for a non-sequential engine; most systems will work on either but sometimes there are subtle things, for example some gert big injector types will overload the gas ECU if run non-sequentially, you'd need their old fashioned slower sister types instead which will perform fine in this application.
I'd recommend one of the cheaper italian injection systems for this, perfectly adequate cos this is not a ridiculously high powered or sophisticated engine by modern standards. OMVL, Zavoli, BiGas, Tartarini are all brands you should get be able to find and get support for. See what your nearest fitter uses, even if you plan to fit it yourself. Don't buy a cheap turkish or polish system you cannot get help or parts for in the future. Don't buy an expensive system thinking it will work any better.
cheers, Ross K