stalls when gassed...

[72grande]

Ok, my friend has a 67 289 with a number of problems that are likely all linked, but we're not at all sure. He has added a 600cmf carb, headers/dual exhaust and an MSD ignition.
Now if he tries to launch the car at all harder than with the flow of trafic, it dies almost uncontrolably. This means no camera catching burn outs or any good racing.
The car also seems to never reach full operating tempurarture. It doesnt matter how long you let it idle or how far you drive it, the temurature always reads cold. He's tested the thermostat.
It also seems to be a gas guzzler even beyond what would be expexted of a 25 year old v-8. Like less thatn 15 MPG on the highway.

My gut tells me it all simply has to do with tuning, but we have no idea how to tune it at all. We've located two screws on the carb that look like they adjust somting, but we are hesitant to touch them lest we make the car worse because we're not sure what the two screws really do. Any help is apreciated.