if you search on 2gnt.com nobody runs a safc on a 420a, some people have and one or two still do but they pretty much hate it.
if you dont like the fmu, which most people running under 8 or so psi use without to much issues on stock injectors, you can step up to the hahn portfueler or if you have the skills to install it you can go megasquirt.

How much boost are you running?