If I understand your question, the Ford 460 distributor is a drop-in swap to the 351-C, although you may have to swap out the drive gear on the bottom for a 351C gear. The 460s wide cap, cone adapter & big rotor simply pulls off and a stock 351C cap & rotor fits in place. This solves the wide-cap-hits-the-firewall bit as well. The early 460 brainbox adapts to the Pantera wiring fairly easily. Your other alternative is a crank-fire ignition, possibly with a 4-coil "distributorless" setup from Electramotive (there's still a stub-distributor to drive the oil pump, though). If the distributor won't set fully down, you likely have the wrong gear, probably a 351W. If run this way, it will destroy your cam gear in 50 miles. Gear spacing is most easily set with the front cover out; the bottom of the distributor hole in the block can be seen if the cam is not installed. There should be "some" clearance between the block & bottom of the gear. Drilling a 0.020" hole in the oil gallery plug just behind the drive gear will add a pressurized oil spray into the gear mesh, prolonging the life of this fragile gear.
