Im rather sure that the SDS systems is allowed .....Ive ran both the fast and the SDS (simple digital systems)-----the fast is a very good system but will set you back plenty of $$$,,,,it will cook for you if you want.......the SDS system is also very good....I like it better...it has a hand held programmer,,,and was VERY easy to install,,,,the ony draw back from the one i had was;;;;;;it did what you told it,,,SO,,if you didnt know anything,,,neither did it
the fast system used O2 sensors to tune and it had an idiot mode,,,you but a basic start point in and toold it to get you 13:1 fuel and thats what it did
I do understand that SDS now offers that option but to be honest with you,,,,,If I were to buy one tomorrow,,,it would be the plain SDS unit and an EGT gauge to tune by
on your question of the stock computer???? in stock you might get away with it,,,,you have real issues with a speed density system on idle and possibly a bigger one with mass air,,,,,,If I understand it correctly,,,a large duration camshaft will play hell with a speed density system ,,,,,,,,,if you just wanted to run the index,,you could do it without popping 1k or so in a computer,,,,,,no need to get a chip,,,,,first thing is to unplugg the distrib from the computer,,,leave the module out so that the computer does not control the timing,,,,if your wanting the tming to move around, do it yourself with a msd unit,,,,use an adjustable fuel regulator and an EGT guage to do your tuning,,,,,,the only issue with doing this is you cant get the best of both worlds with the fuel curve,,,,,believe it or not,,,your car will use less fuel at higher RPM,,,,so either you starve it thru the mid range to have it tuned inupper RPM OR you run it rich on top end to give it the fuel it needs thru the mid range
on my little mustang,,,the SDS was worth about .30 VS the stock computer,,,,,dont know about SDS vs fast,,,they were on 2 different cars
here is the WEB site for SDS----they sell a harnas that directly wires into the mustangs existing harness by just unplugging the computer and run a couple of wires
http://sdsefi.com/
here is the company I bought mine from....no issues
http://www.wmsracing.com/
good luck