I fly behind an o-320 B2c which has the conical mounts. No problem!
Some say that there is more vibration transmitted to the airframe from the engine, but that has not been a problem for me, and I used the extra $5,000 I save on my panel!!!!
The conical mount will keep the engine stiffer in the cowl, but transfer more vibes to the airframe. The Dynofocal is a absorbs more vibration, but moves around a lot.
Use the search function at top of page, there is lots of info already, (type in: conical dynafocal) cheers.
Bottom line Dynafocal is better in every way and preferred. Physically the geometry of the engine mount and design of the vibration isolators are totally different. They are not interchangeable**.
Used older 320 engines, which you can get cheaper, often have conical mounts. There have been no new Lycs made with conical mounts for a long long time. That should tell you something. However if a conical 320 comes into your life its nothing to fear.
Unless you are going to buy an old Lyc 320, its a moot point. However conical works fine, especially if you're getting an good deal on an engine or RV, however if possible always go dynafocal.
** During complete engine overhaul you can convert a 320's conical engine mount to dynafocal for a not totally unreasonable extra charge. (ECI does the conversion)
If you have a conical mount case and you prefer dynafocal, it can be easily converted for a reasonable price. Contact one of the inspection and repair shops like Divco or Crankcase Services for details.