hi have a few questions
just bought a 66 mustang gt 289 4v 4 speed
have checked the block and it reads 6C12 march 12 1966
i am trying to find out if heads are correct
casting numbers on heads are as follows
one side has No:10 and the Other No:11
also has C6AE-289 and also WF6k17 on one the other WF6k18
are the 289 heads 4v , what do i have to look for to verify they are 4V

 

I'm pretty sure the only thing that was changed on 289 GT engines was the intake manifold.

 

My understanding is that the GT option was more cosmetic. You could order C, A and K code engines at 200, 225 and 271hp respectivelyin a GT coupe, vert or fastback. The demand was so great that factory production couldnt keep up and a lot of cars had GT options added at the dealership...genuine GT or not??? The number of restos made to look like GTs adds to the difficulty of identifying genuine cars.

raven, IMO what you need is to identify the genuine K code engine which was not specific to the GT.
try http://www.midcomustang.com/mustanghipo.shtmlasa starting point

good luck