I used to make these back when i was an Amiga dealer. We used them to convert pc minitowers into external SCSI boxes. You could get the stuff at Radio Shack for the most part, although it may no longer be true. They made a small circuit board that was a match for one of their prototyping boards.
radio shackIf you look at that board, you see two common strips down the middle of the board. All of the pins on one side of the idc50 are ground except one. so if you isolate that pin on the board, you can solder idc50 there. Then it gives easy access to all the pins on the other side. Then you get a short DB25 cable - making sure it has all 25 pins... cut it in half and wire it to the proper pins of the IDC50. Use a standard internal scsi ribbon cable to connect to the drive & you're done.
easier to do than to describe. ;-)