the ford racing stg2’s SUCK for boost. theres not enough valve overlap to be able to pressurize the combustion chamber long enough, and when you try to dial in the cams via cam gears it throws everything out of whack.
ive never even HEARD of SPA turbo kits, but good luck on that one. you dont need the diablo mafia, you can buy a mustang maf and have it calibrated via the sct tuner and it will work perfect for hundreds cheaper. the ford racing head is quality but can be improved upon greatly. for 1k, the head should produce more power than it does.
ive been down this road before with a 2003 zetec 5 speed focus. had every bolt on plus a set of FR stg2’s… (made 117hp/134tq @ synapse) ran 15.567 @ 86.51mph…(for reference my sti trapped faster at the 1/8th than my focus did in the 1/4) traded the car in and never looked back. id want more than 150-160whp out of the head and cams and bolt ons, but you just wont see it. save your $ on all that and buy the “powerworks” supercharger for it (with the big boost kit), do the svt header, random-tech highflow cat and a 2.5" trubendz borla exhaust (www.trubendz.com) and it will make around 285-300whp and you will have spent less and be happier with your investment… by all means if you want to do it this way go for it but you will be very disappointed in the end result i think.