Never posted on this forum before bur, here goes. I have always understood, like Dan Winterland, that a major disadvantage of tail mounted engines was the extra weight to compensate for so much concentrated on the (almost) centre line. An additional disadvantage is that, to keep the cg where it should be, the wings had to be a long way back thus reducing the tail moment. This requires a larger stabiliser to maintain its required power. Thus more drag. You have to admit the VC10 tailplane is a bit big. The BAC111 accident taught us that T tails are prone to locked-in stalls. There is always that danger despite some getting away with it. Hence the requirement to have a recovery parachute during trials of such configurations.