I keep three CS-3400 in my truck. It's time to get them ready for the busy season. I run into couple CS-3450 saws in the local ads here for cheap, but the engines are in top shape. Wondering if they have the same engine and everything except the top handle parts. If I buy them, what's involved to swap parts from one of my old 3400 to make a new 3400. Thx.