I may have to read up on the subject at what compression is ideal, but I'm guesssing it's between 15:1 and 18:1 without having to worry about preignition on diesel.
Uhh try 24:1 for good diesel performance, these aluminum
heads can't take that much compression, as well as the shape
is wrong. Diesel heads need almost no CCs and are built as
flat as they can, the pistons are made of cast iron in heavy
diesel engines, I don't know what is being used in the smaller
engines, and the piston shape has a doughnut shape hollow
with a tit in the center, the fuel ignites in the hollow.
If you go lower compression, like 15:1 or even 18:1 you will
need glow plugs to get it started. In short, you need a custom
head and then the block would probably not hold up.