What you meant to say is "You won't get much more power out of that engine easily But you're right in as much as they weren't popular for tuning because there were plenty of Pinto and YB engines with tuning options available at the time - the poor I4 was overlooked.

The Superchips chips plug onto the expansion/diagnostic connection on the side of the ECU. Ebay's the best bet for these - not sure if Collins still produce them.

Apart from overheating from dodgy fan switches, these engines are reasonably bullet (and idiot) proof.

K&N 57i directly on the end of the inlet manifold is a good bet, and as said, the Ashley exhaust also helps add a bit of grunt.