This opcode went through a couple of changes. Versions of mldonkey starting with 2.5.17 send the following:
|int32||The maximum protocol version accepted by the core|
|int32||Maximum Opcode value sent to the gui (e.g. 58)|
|int32||Maximum Opcode value accepted by the core (e.g. 67)|
Versions numbered 2.5.15 and older don't send the last two int32s:
|int32||The maximal protocol version accepted by the core|
Version 2.5.16 has an "if" statement in the opcode definition which states that if the protocol version is >25, it'll send the other two int32s, and if not then it won't. However, looking at the code, it looks like the protocol version at the time the code is executed will always be zero. So there's a good chance that 2.5.16 will never send the extra two int values. Not having a 2.5.16 version available anywhere, I'm not 100% sure though.
Best Protocol Version for MLD 2.7.4 is 40 (from ./src/daemon/common/guiProto.ml)