I don't know what Modified F class is, but have been to a couple of shoots just to watch. in talking to some competitors, they were glad to show their rifles and tell me the brand of barrel, action, stock etc. but nobody said how much they spent. I'm sure it's more than I want to spend.
once while shooting my rem 581 with aquila HVHP, I shot a .280 group
what I'm saying is, that those guys who are serious competitors with their custom guns are going to win. I'm sure that there are some with a lot of money and no talent, but they don't last long in competition.
I for one, would not put a stock rifle up against them.