I'm a diehard fan of the 340/360 head! and with a little work you can make good ### BUT even i have fallen from the stock head. I went with a set of RHS head with my last build. I can make a 340/360 head flow as much or more then a RHS head prepped with a 2.02. BUT for the same flow (CFM) the rhs will outperform the stock head.(better port shape,(velocity) that you can't make without finding coolant passage or so close they crack)
The short answer........If you need to put guides in the heads, building ANYthing over stock. RHS iron heads is cheaper in the long run, and more power.