I have a PIMPXS in my turbo Fox, it's still a speed density system. I like it, the support forum is really helpful. The MSPNP is a speed density system too, I've heard its similar to the PIMP and I have also heard the forums are pretty good. If you already have a standalone system in mind, I'd get the nastiest cam that you can get, considering there will be engine management at some point, and a cam swap is basically tearing the engine half apart.
Speed density system is very forgiving. The people that hate on it ain't ever rocked with it. My 85 Marquis has the most preliminary EEC-IV speed density ECM which runs two injectors on a throttle body unit. Everyone on the Marquis forums said that ECM would never handle a head swap or an intake swap or exhaust mods, and we've done all of those things, daily driving still. I'd say just throw what you got at it.