I got both a Mule set and a Riff Raff neck (for another guitar).
Both will lead you into the Slash territory. The Riff Raff and Mule neck are close when recording them. The Riff Raff has just a touch more treble bite, a touch less round and sweet tone, but they are very close . A touch more rock for Riff Raff neck, a bit more blues for Mule neck.
For what you want, I can't imagine another choice than a Set of Mule (Alnico IV).