I asked about this precise way of mounting engines due to a thread posted back in 1998 model boats.
it seems that vertical mounts is just mainly for the old multi class boats.
the majority of offshore boats use horizontal mounting to their rails.
I fitted some wooden rails to my boat and have had no problems at all.
rather than just sitting on 4 posts, the mounting is spread a lot more giving a strong brace after
the rubbers have done their work in reducing vibration also making it a quieter mounting system.
The wooden rails also take a fair bit of shock away.
Years ago we all mounted the solid way,flat plates bolted directly to engine then to a solid mount of fibreglass.
a few broken crank cases maybe, but i never got one.
I dont think i would ever mount solid again and take the chance.
The majority of spark ignition boats use rail mounting as well.
so maybe both ways is good, a good point to think about though.
below is 2 other examples, 1 horizontal, and 1 vertical. both very good.
phill