I have removed my 502 mag from my boat and am wondering if i need to upgrade to offshore mounts when i install my ne 500HP or will stock motor mounts work fine??

Stock will "work" but I would switch to a offshore mount for the front.

just curious..what is the ''crossing'' point from the boat builders...at what hp rating do they start to install the hd mounts?
i went from 454 mag mpi to 496/whipple i would like to know what i have in the boat

When i dropped the HP in my Warlock i used a Gill offshore cradle . By doing this you tie the stringers together and make one very solid mount . NO chance of the stringers spreading and cracking in rough conditions or wave jumping . IMO all boats with moderate to high horsepower should be done this way . Torquing loose from the stringers can't be pretty !!

Stock mounts will work as long as they are not lag bolted but actually through bolted to the stringers. Most manufacturers will use the offshore plates on 500hp or above.

thanks