Think of the 405 as a 531 head, the only difference is the spark plugs are pointed/placed less optimally. Basically means it is a little more prone to knock under performance situations, however with ethanol fuels and what not, it is not an issue these days...
If the head is from a 240 it will be kjet. So if your running EFI, you just need to buy or make up some kjet injector plugs. STS machining sells them. The 405 from early 740 turbos will not need these as they are EFI to begin with.
The small/big coolant passage thing is only a problem if your running big boost... Even then you can combat that with metal head gaskets. The 240 head will be big coolant passage, the 740 head will be small coolant passage.