Interesting differences between the Deltahawk and the SMA diesel engines.
First, the Deltahawk is a 2-stroke, while the SMA is a 4-stroke. This yields best BSFC figures of .39/lb/hp/hr for the Deltahawk, and .35lb/hp/hr for the SMA. The Deltahawk has a very strong torque curve, but you would expect that from a 2-stroke engine. That could be useful in a helo application.
The Deltahawk is a V4 while the SMA is a flat 4. This makes the Deltahawk more compact and lighter (it's also lower powered so it's lighter for that reason as well). However the Deltahawk is liquid cooled and requires a radiator, while the SMA is air cooled. I'm not sure how well a radiator on a piston helo would work out though.