Here's what I did electronics-wise:
Swapped in MAF computer
Added a stock MAF sensor from a 5.0L Mustang
Installed 24# injectors
I am not saying that the diagram on the site is gospel, but it looks like he is going to have to do a few minor wiring mods in order to keep the ability to pull codes.
See: C. EXAMPLE OF A PIN OUT COMPARISON BY NUMBER BETWEEN AN '86/'87 SPEED DENSITY SYSTEM '90 MAF SYSTEM
http://therangerstation.com/tech_library/MAF_Conversion.html
He still needs the pins and the plug for the MAS, consider hitting the junk yard for the MAS pins, wiring and plug for the MAS from a early 90's Stang or similar. (You might need to get the entire harness, it takes a while to dig it out) I used off a '93 HO harness. Ford Dealership part dept will need to see example pins (be prepared), or I believe they can be purchased from Ebay.
And it's strange that the 2.9L ran fine with the 24# injectors. I ran into problems with 19s at idle. I used an IST Air Adjust that's mentioned on that page to somewhat compensate for it. Maybe it was just the MAS I used? It was from a 3.8L Taurus, but I also tried a 65mm MAS from a Stang with similar results. I ended up just giving the Stang MAS to a friend of mine that was trying to diagonse a problem.
Pete