I can understand about trying to avoid a dyno tune.
The chance of you having BEST power AND drivability on a blown combo without a tune is pretty slim.
As was talked about above ... the fmu thing can be used but if anything goes wrong .................
you have lost a head gasket at least and maybe motor damage.
1 The GT uses 19's and the Cobra uses 24's
2 The GT and Cobra use the very same maf
3 The GT and Cobra use different pcm's
Lets deal with 3 first
The pcm you now got is fine and can be tuned just as good as any other pcm. The is no need to go to a different one.
Now for 1
19's or 24's ... makes no difference ... They are too small
UNLESS
you use a fmu and run mega elevated pressures
You do what you think is best but if you'll look on the power adder forums you'll find tons of peeps who moved away from the fmu thing for a reason.
As for 24's supporting 400 hp ..........................
Consider these thoughts about that kind of reasoning
400 fwhp is only around 330-340 rwhp
You got a blower pulling down more of that hp as well
You also gotta remember that fuel is needed to cool the charge a bit in a blown combo which means more fuel still
24's are too small for what you want to do
Lets move on to 2
The maf takes the air that passes through it and converts it to a voltage.
The GT or Cobra will not pass enough air to cause a prob when stock.
Even with a few mods the stock maf is gonna be just fine.
Now with what you are tryin to do ...............................
Your blower is gonna cram way more air past the maf than it knows what to do with. The only thing it can do is tell the pcm it is maxed out. This happening is most likely gonna happen at about 50 to 75% of your rpm range.
You then will go lean
OR
maybe you have heard peeps talk about "pegging the maf"
You really don't wanna he able to tell peeps you did that ... even more so with a blown combo. Head gaskets, pistons, or rings may be damaged when that happens
I can totally understand where you are coming from
I'm not trying say a custom tune is a must have
I am trying to say many other blown peeps have tried fmu's, C&L mafs or other mafs for that matter that are too small and finally just got sick & tired of the whole mechanical method of tuning and went with a chip burned by a Pro.
Good luck with which ever way you decided to go
Grady