Quarter mile in 7 seconds?
A McClaren F1 (fastest street car made) can do it 11.1 seconds at 138mph and weighs a fraction of an old Magnum. (The May 1978 issue of Road & Track listed the car they tested at 4,312lbs. The April 1978 issue of Car & Driver listed their Magnum XE test car at a weight of 4300 lbs even...by comparison, the F! weighs 2,341 lbs...around half the weight of a Magnum.
So you are saying you could beat a McLaren in the quarter mile and still have time to change the radio station a few times before he caught up to you?
BTW, using the 1/4 mile time and mph you supplied combined with the weight of the car (plus a 150lb driver) the hp calculation is:
Using the ET method, I come up with 2564 horsepower
Using the Speed method, I come up with 1767 horsepower