can i change the 5163d to an internal, if so would not the ide interface give a higher and more reliable transfer rate
Yes, you should be able to use the drive inside the 5163D internally. Inside the 5163D should be a 4163B. I am not sure you whether you will get a more reliable transfer rate because I don’t know what your system’s setup is like. However, you should be able to hit 16x reliably with a decent setup when the drive is connected internally. It can’t hurt to try anyway, since if you don’t like the results, you can always put the drive back into its external enclosure.