It is possible to convert a stainless frame to DAK, but it takes some ‘smithing. Bruce Gray converted at least one. This was gleaned from the SIG forum hosted on the “Eve” network. The relevant posts would be ‘way, ‘way back in the archives, by now. If anything has changed, since then, I am not aware of it.
Keep in mind that DAK is not a simple DAO conversion. Frames made before a specific date are not convertible. There are simpler DAO SIGs, but I their trigger pulls are notably quite heavy.
http://sigforum.com/eve/forums