They also have to abide by class rules which restrict what type of motors/suspension/chassis etc... I mean hell, NASCAR motors are dinosaurs but they run them because that is what NASCAR says they have to run. If they were simply limited by displacement you'd see crazy OHC, variable valve timed tech crazy motors.
There are some very big power 2Vs out there too, think 900+ with the TFS heads but the parts are so expensive its not cost effective at all IMO. Just a set of TFS heads and cams alone for a 2V cost more than a whole Coyote pullout or an entire LSx/Trans combo.
2000 Mustang GT Steeda #0048 34k miles. 99 Cobra 4V swapped, FTBR IRS swapped, exhaust, tuned by James Gordon.
Just because I give you advice, doesn't mean I know more than you. Its just means I've done more stupid ****.