having also done the research on this it'* sorta a waste. Buy an SSEi, a chip, and a pulley from a hardware store... SSEi ($3500) + Chip ($300) + Pulley ($5) = $3805 and that'll be a nice daily driver.
FWD + "Serious" hp = Bad Mojo. It'* hard to stop the Torque Steer on a 300 hp FWD car. 400 is nearly impossible.... especially with a 5-speed FWD, but that'* a different story.
And honestly if you're going to build a race car, don't start with an H-body. They're about 3 feet too long and a 1000 lbs too heavy.
This coming from a guy who used to race Tauruses ... which are a little lighter, but still have the same detriment. Furthermore, you'll be making serious upgrades to support the really high output of the GNX plant. The fuel system just won't be able to take it. And assuming you either wire up a stand-alone Fuel Injection system, you'll have that added cost. OR, you'll have to patch the GNX computer into the old bonneville wiring harness and I don't think the two electrical systems are similiar ... so you'll have a real patchwork job there. Don't for get new exhaust! You'll need to put at least 3" single exhaust out the back.
If you find a GNX Engine, find a G-body (Is that it for those Monte'* and Regals? Or is it A-body? **** it, I'm a ford guy, LOL) with a standard V6. Drop it in, hell add a 5-speed if you want, wire up the computer and go to town.
GNX Engine w/ Wiring and Computer = $500 in these parts (sometimes more)
G or A body (I don't know which f-ing one it is) = $1200 in nice shape with a V6
new exhaust = $600
So for, about $2300 you'd be running 12'* with a nice set of sticky tires. That'* not so possible in a Bonneville. :(
I hate being the local skeptic ... but uh ... yeah ... I'm going to stick with my position that Bonnevilles are great daily drivers but not so great Race Cars.