The mod that Gill is referring to is commonly done. It is an FAA approved process. I wouldn't be concerned with strength issues as long as the mod was done by a certified case overhaul facility to certified standards. I have never seen a case either modified or not, crack in the area in question. That includes engines that have been involved in hard impact crashes. The tubular mount most always breaks first. If you are overhauling the engine and you don?t have an engine mount yet I would highly recommend getting the case changed over. The perceived vibration in the aircraft, with a dynafocal one setup is less than with a conical setup.
Good Luck,
Mahlon