Helicopter engines rate the power differently.
My RV-8 has an IVO-360A1A, converted. It's rated at 180 HP @ 2900 rpm at 1500 feet above sea level IIRC. Power loss with altitude could be the difference, also SAE rated horsepower can be 5% low, so an aircraft engine rated 180 HP can be delivered to the customer if it only puts out 171 HP.
Horsepower to a helicopter is a more profound factor so i think horsepower ratings are more carefully and accurately described. you can see the similarity if you compare operating manuals.
My vertical engine conversion required a gear case, a magneto idler gear, and a sump. I went with a Superior aluminum cold air sump, the were $1300 at the time, lighter weight and better price.
The Bendix 200 mags were re-used. The Bendix fuel injection was missing parts, so I don't know how re-usable it was, I went with Airflow Performance injection and didn't look back.
Vans provided the conical engine mount, it was built by Bruce MacIntyre in his fabrication shop in Tacoma WA.
I bought VANs cooling baffle kit. Helicopter engines need aircraft baffles. add that consideration, also it takes a few days work to assemble.
An interesting difference, there is an oil tube from the crankcase oil gallery along the tappets to the head of each cylinder. they circulate oil around the exhaust guides and dump into the rocker box. I run with cool head temperatures. Seeing this when I bought the engine, I went with the 10 row experimental aircraft oil cooler.
I'm totally satisfied.