Came across this auction coming up in 12 days...

Chassis No. THPNMA05855
Estimate: £190,000-£240,000 (that's between 300-400K USD)
AUCTION DATE: Wednesday, October 28, 2009

1974 De Tomaso Pantera Gr. 4 Competition Coupé

There's a long writeup about the car and a little history on Group 3s and 4s in general - an excerpt about this car:
"Initially built to Group 3 specifications, chassis number 05855 was completed in 1974, then brought back to the factory to be converted to the more aggressive Group 4 level of preparation in 1975. It retains the 5.8-litre Ford V8, but unlike the first series of Group 4 Panteras, it’s fed by four Weber 48IDA twin-choke carburettors and fired by a Magnetti Marelli ignition system. So equipped, the engine is rated for 560 horsepower. In a car weighing less than 2,600 pounds, this yields some impressive performance numbers – comparable to, and in some cases exceeding, those of a Ford GT40."

There's also a bit of history and some photos on the QV500 site - http://www.qv500.com/detomasoregistrypangr305855.php