I'm in the process of doing a makeover to the H9 Twotter. I am making a DHC6-100 instead of the -300. I did quite a bit of research on engines so hopefully you can benefit. Since I am recovering/glassing/painting, I was not confident the Saitos 40's would perform with the increased weight. The FA-40 appears to be the only 4 stroke engine that will fit without modification.
Below is what I found. I elected to go with the Saito FA62A's since they are in the same case as the FA56, and I already own one of the required 2. I also extend the cowl instead of cutting into the firewall as I also increased tank size from the standard 8oz tank to 10oz. The line of the prop still appears to be in line with the fuse in a scale location. I'll post pics when I get some.
Disclaimer.... the dims for the Magnum below is the best I could determine. Info for that engine is hard to find.
Below is my target model
