Mustang 65 and Corsar

Hello, how are you all, I have some technical questions and I would like some of you. They will help me.
I have a client who has a Mustang 65 and make time I change the trans. Aut. For a more modern one, the box he put was a Ford Metric with Over Drive, but the problem is that the car does not develop what it should, since I imagine that it must be because of the differential passage, I would know if someone has some information regarding the passage of the differential they must take to get it. Thank you I wait for your comments.

I do not know what country you are, so I imagine that that Stang has a 289 or 302, the important thing is that the transmission has, I do not know that you measure it, but in the US Transmission, do you need to know what relationships do you have and you have?, if the engine is heated? And for my opinion that original C4 box is very good and easy to repair, it is only modified with a trans-power and it is perfect, the ideal for today would be to put one of 9 \ "that surely has a 8 \" They are not to use daily are to step hard and have fun with them, in my family there are 2, all and modified.

To have an idea, put the rear rudeas in the air and turn the rudes telling the cardan's turns, the best would be to take out the group and see q number has, if it does not heat the machine and it reaches 210 that car is good, if you want more torque that it puts Camarin Torquer and Header shorts apart from a holley 450, to walk correctly, without that those engines are disgusting, apart from a dual belly With oil. Let me know when you know if the engine is heated and you have a transmission. (A box that put is not bad, just that the torque is more elastic, that puts more power to the plaster machine will be decent, explain to it: before it had shorter legs faster but less pointing speed now longer so long as slower but more peak speed)