Plus MAF has 9 injectors and Speed has only 8, and different wire harness. They went back to MAF in '93. 9th is for cold running (choke), speed adds to all injectors for cold running. Some like MAF, some like Speed Density, I have Speed, I don't like the looks of the MAF sensor, and I run a K/N nose filter on my MPI, I have converted my Hilborn to Speed Density with electronic injectors. MAF will learn things you add to the motor, Speed will need a new chip if you change the motor vacuum with a cam. Chips these days are everwhere, and cheap to have burned.
There is more to them, but thats the easy way to say it.

Pat