I went through a ton of different options trying to convert my a51:S4 cab.
My advice is google search your specific cab first!
Some cabs will accept adapters some wont!
Mine would not accept a IDE to SD/CF adapter but a regular A51 cab will.
I did get a flash solution for mine in the end that consisted of using a IDE to SATA adapter then using a SATA memory module which works perfect.