GW used generic names for the paints in the MoM Hobby Set and the older MoM paint set and I'm not sure if they ever actually had equivalents in the Citadel paint range. Additionally, as you know, the paint range has been completely overhauled, so getting an equivalent of an equivalent is more difficult.
But yes--Bestial Brown (now Mournfang Brown) is almost certainly the best equivalent of the Brown they included in these sets.
If you're looking to restock on paints, I'd recommend switching to Vallejo, which are of a much higher quality (and cheaper) than Citadel paints. The eye-dropper bottle makes them ideal for paint palettes.
Here's a compatibility chart comparing Old Citadel and New Citadel with other paint ranges. Try and see if you can match up your colors there.
http://www.dakkadakka.com/wiki/en/Paint_Range_Compatibility_Chart