The 913 head can be milled .090" to get the same compression ratio as an 848 head, but a few other modifications need to be done, like recessing the intake valves the same distance, shimming under the rocker arm stands, and adding lash caps between the exhaust valve stems and the rocker arms. None of that is particularly difficult, but the parts-swappers of today usually don't have the technical ability to do such things. If it's not a bolt-on swap they claim "That's impossible!" Too bad!
Jerry
