The Cobra's runners are almost an exact match to the P heads. I checked mine and is almost perfect (Fel-Pro 1250 gasket). I think the runners on the TFS would be too big unless you want to do any grinding on the heads. I think overall the Cobra costs less (find used for $300 and has built-in EGR) and is a better match to your parts. There is a lot to be gained in having matched parts.
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1991 Mustang GT - Cobra Intake, FMS 65mm TB, C&L 73mm MAF, GT-40P heads, Crane 2031 cam, Crane 1.7rr, Built AOD, Art Carr 2400 non-lockup converter, Transgo shift kit, BBK chrome cold air, FMS 'P' headers, Pacesetter off-road H, BBK aluminum pulleys, 2-C Flows w/ dumps, 4.10's, Steeda STB, for now...
The Original GT-40P Tech Page