March is a really good time for Castaic. I don't know about a double digit fish though. I just caught a 12.29lber two weeks ago during a club tourney and from what I am hearing that is one of the largest fish to come out of that lake in years! So if you are after double digit fish I would recommend Casitas instead or go down to the Castaic lower lagoon which has a lot of big fish.

As for guides, I have heard alot of negative stuff about Troy (Not knocking Troy) so I can't recommend him but Gerry Mahuia is an awesome guide out of Mission Viejo and has a good rep if your mind is set on Castaic. His website is www.catchmorebass.com But if you want to go to Casitas then maybe the Ojaiangler guide would be a better choice.

Hope this helps.