Use the gt40p's. From my understanding, the 351w head is essentially the same thing as the e7 head. Plus you'll get better spark distribution with the p's. Unless the head had the valve pocket machined, then they probably aren't dual springs.
1995 Mustang GT
1999 F150 Lariat 4x4
Soon to come: 393 stroker
351w bored .030, Probe Industries forged internals, Trickflow 205's, FTI custom cam, Trickflow R 90mm intake, Accufab 90mm TB, FRPP 42lb injectors, 1 3/4" custom Accufab LT's, 3" exhaust, MS2