If you care to compare specs, here's the GM story:
http://www.chevrolet.com/performance...gines/ls9.html
...and here's the Trinity tale:
http://www.mustangandfords.com/news/...8/viewall.html
For those concerned about me fouling the water by mentioning the Raptor 6.2, perhaps we'll share this, together, from the above article:
Nor could they move over to the bigger architecture of the 6.2 V-8 as found in the SVT Raptor. That engine is too large for the Mustang engine compartment, plus it would be prohibitively expensive to design a better breathing Four-Valve cylinder head for it, as well.
As with all things involving motorsports,
"Speed costs. How fast did you wanna go?!"