I swapped everything (engine , trans, rear axle) from a '70 Mach 1 with 351 into my ex-wifes '68 Mustang coupe. Bolted right in, but I don't know if the '66 has room between the towers. Up until that point I was not really a Ford guy, but that 351 changed my mind.

At $ 800 you have nothing to lose.

Don